Drive axle system having a clutching device

ABSTRACT

A drive axle system for a vehicle drive train having a clutching device is provided. The drive axle system includes a first shaft, a bevel gear inter-axle differential, a first axle assembly, a second axle assembly, a first clutching device, and a second clutching device. The first axle assembly is drivingly engaged with the first shaft. The first clutching device divides one of a pair of output axles into first and second portions. The second clutching device selectively engages a driving gear of the second axle assembly with a portion of the bevel gear inter-axle differential.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/135,989 filed on Jul. 20, 2011, which is incorporated byreference in its entirety. The present application is being filed duringthe pendency of U.S. application Ser. No. 13/135,989.

FIELD OF THE INVENTION

The present invention relates to a vehicle drive train and a drive axlesystem for the vehicle drive train having a clutching device.

BACKGROUND OF THE INVENTION

Vehicles incorporating multiple drive axles benefit in many ways overvehicles having a single driven axle. Drive axle systems in suchvehicles may be configured to distribute torque proportionately ordisproportionately between the axles. Additionally, shift mechanisms maybe provided to such vehicles to permit the disengagement of one of thedriven axles, and to transition from single axle operation to multipleaxle operation during normal vehicle operation, among other benefits.However, such versatility typically requires the incorporation ofadditional drive train components into the vehicle at added expense andweight. Such added weight results in a decreased fuel efficiency of thevehicle.

Clutching devices in such drive axle systems also need to be selectedbased on a gear reduction ratio present in a wheel differential. Axleratios may be of a two-speed configuration to permit the vehicle tooperate in a low speed and high torque manner or in a high speed and lowtorque manner. It is preferred to drive multiple axles when the lowspeed and high torque manner of operation is desired (to distribute thehigher torque amongst a greater number of wheels) and it is advantageousto operate a single axle when the high speed and low torque manner ofoperation is desired (to decrease windage and frictional losses whentorque distribution is of lower concern). However, incorporation of boththe two-speed configuration, an axle disconnect function, and aninter-axle differential may be prohibitive with respect to cost andweight. Such added weight, windage losses, and frictional losses resultin a decreased fuel efficiency of the vehicle.

When multiple axles of a drive axle system having the inter-axledifferential are operated in the low speed and high torque manner ofoperation, torque output at each of the axles should optimally be equalto prevent slippage of the axle having a greater torque. The inter-axledifferential having a planetary style differential, by design, unequallydivides torque. As a result, the inter-axle differential having theplanetary style differential, when used with multiple drive axles havingsimilar axle ratios, can slip as a result of unequal torque distributionwhen the vehicle having the inter-axle differential is operated on a lowfriction surface.

It would be advantageous to develop a drive axle system that islightweight, reduces windage and frictional losses, can be operated in alow speed and high torque manner of operation and a high speed and lowtorque manner of operation without excessively increasing a cost of thedrive axle system.

SUMMARY OF THE INVENTION

Presently provided by the invention, a drive axle system that islightweight, reduces windage and frictional losses, can be operated in alow speed and high torque manner of operation and a high speed and lowtorque manner of operation without excessively increasing a cost of thedrive axle system, has surprisingly been discovered.

In one embodiment, the present invention is directed to a drive axlesystem comprising a first shaft, a bevel gear inter-axle differential, afirst axle assembly, a second axle assembly, a first clutching device,and a second clutching device. The first shaft comprises at least oneshaft section. The bevel gear inter-axle differential comprises a firstside gear, a driving spider, and a second side gear, the driving spiderdrivingly engaged with the first shaft. The first axle assemblycomprises a first wheel differential, a first driving gear, and a firstpair of output axles. The first driving gear is coupled to the firstwheel differential and drivingly engaged with the first shaft. The firstpair of output axles is drivingly engaged with the first wheeldifferential. The second axle assembly comprises a second wheeldifferential, a second driving gear, a second pair of output axles, anda first clutching device. The second driving gear is coupled to thesecond wheel differential. The second pair of output axles are drivinglyengaged with the second wheel differential. The first clutching deviceis disposed on and divides one of the second pair of output axles intofirst and second portions. The second clutching device has at least afirst position and a second position. The second clutching device in thefirst position drivingly engages the second driving gear with the firstside gear of the bevel gear inter-axle differential and the secondclutching device in the second position drivingly engages the first sidegear of the bevel gear inter-axle differential with the driving spiderof the bevel gear inter-axle differential.

Various aspects of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other advantages of the present invention, willbecome readily apparent to those skilled in the art from the followingdetailed description when considered in the light of the accompanyingdrawings in which:

FIG. 1 is a schematic view of a drive axle system according to anembodiment of the present invention;

FIG. 2 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 3 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 4 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 5 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 6 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 7 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 8 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 9 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 10 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 11 is a schematic view of a drive axle system according to anotherembodiment of the present invention;

FIG. 12 is a schematic view of a drive axle system according to anotherembodiment of the present invention; and

FIG. 13 is a schematic view of a drive axle system according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the invention may assume various alternativeorientations and step sequences, except where expressly specified to thecontrary. It is also to be understood that the specific devices andprocesses illustrated in the attached drawings, and described in thefollowing specification are simply exemplary embodiments of theinventive concepts defined in the appended claims. Hence, specificdimensions, directions or other physical characteristics relating to theembodiments disclosed are not to be considered as limiting, unless theclaims expressly state otherwise.

Turning now to FIG. 1, a drive axle system 100 is shown consisting of afirst axle assembly 102 and a second axle assembly 104. An input sourceof rotational energy is provided to turn a first pinion shaft 106 of thefirst axle assembly 102. One or more bearings 108 may be located incontact with the first pinion shaft 106 to enable it to rotate within afirst axle assembly housing 110. The first pinion shaft 106 has a firstpinion gear 112 mounted thereto. The first pinion gear 112 has a toothedportion. The toothed portion is engaged with the forward side of atoothed portion of a first axle driving gear 114, also located withinthe first axle assembly housing 110. The first pinion gear 112 may besuch as a hypoid pinion gear. The first pinion shaft 106 is drivinglyengaged with the first axle driving gear 114 of the first axle assembly102 through a single gear mesh.

The first axle driving gear 114 is mounted on, or connected, to a firstwheel differential case 116. At least two pinion gears 118 and at leasttwo side gears 120 are located within the first wheel differential case116. As known by those skilled in the art, the pinion gears 118 and theside gears 120 are connected to one another. The side gears 120 are alsoconnected to axle half shafts 122. The axle half shafts 122 extend fromthe first wheel differential case 116 and the first axle assemblyhousing 110 to a wheel end 124. The wheel ends 124 supports wheels andtires (not shown).

A second pinion gear 126 with a toothed portion is engaged with arearward side of the toothed portion of the first axle driving gear 114.The second pinion gear 126 is mounted to a second pinion shaft 128. Thesecond pinion shaft 128 is mounted on the at least one bearing 108 tofacilitate rotation of the second pinion shaft 128 within the first axleassembly housing 110. The second pinion gear 126 may be a hypoid piniongear.

The second pinion shaft 128 comprises a plurality of splines formed onthe shaft opposite the second pinion gear 126. A splined sleeve 130 maybe engaged with the splines on the second pinion shaft 128. A firstplurality of axially moveable discs 132 may be located on an outersurface of the splined sleeve 130.

A second plurality of axially movable discs 134 is located on aninterior surface of a clutch bowl 136. The clutch bowl 136 is locatedradially outward in a concentric fashion from the splined sleeve 130.

The clutch bowl 136 is connected to a neck 138. One or more bearings 108may be located between the neck 138 and the first axle assembly housing110 to facilitate rotation of the neck 138, and thus the clutch bowl136, within the first axle assembly housing 110.

The first plurality of axially moveable discs 132 and the secondplurality of axially moveable discs 134 may be selectively compressed soas to couple the clutch bowl 136 and the second pinion shaft 128. Theselective compression is applied by an actuator 140. The actuator 140may be a pneumatic actuator, an electromechanical actuator or ahydraulic actuator. Any of the foregoing may be connected to a vehicleanti-lock braking system to facilitate further vehicle control via thedriveline. The splined sleeve 130, the first plurality of axiallymoveable discs 132, the second plurality of axially moveable discs 134,and the clutch bowl 136 form an inter-axle clutch 141.

The neck 138 is connected to a first yoke (not shown). The first yoke isconnected to a propeller shaft 142, such as through a first universaljoint 144. The propeller shaft 142 is connected to a second universaljoint 146 located on the second axle assembly 104.

The second universal joint 146 is connected to a third pinion shaft 148.A third pinion gear 150 is connected to the third pinion shaft 148. Thethird pinion shaft 148, and thus the third pinion gear 150, is mountedfor rotation within a second wheel differential housing 152. The thirdpinion gear 150 may be such as a spiral bevel, or it may be a hypoid.

The third pinion gear 150 has a toothed portion that is engaged with atoothed portion of a second axle driving gear 154. The second axledriving gear 154 is mounted on, or connected, to a second wheeldifferential case 156. At least two pinion gears 158 and at least twoside gears 160 are located within the second wheel differential case156. As known by those skilled in the art, the pinion gears 158 and theside gears 160 are connected to one another. The side gears are alsoconnected to axle half shafts 162. The axle half shafts 162 extend fromthe second wheel differential case 156, and the second wheeldifferential housing 152, to a wheel end 164. The wheel end 164 supportswheels and tires (not shown).

The second axle driving gear 154 may have a smaller diameter than thefirst axle driving gear 114. By way of example only, the first axledriving gear 114 may have a diameter of approximately 18 inches, whilethe second axle driving gear 154 may have a diameter of approximately16.5 inches. The purpose of a difference between the diameter of thefirst axle driving gear 114 and the diameter of the second axle drivinggear 154 is described below.

A shaft clutch 166 is mounted to one of the axle half shafts 162 anddivides the axle half shaft 162 into a first portion 168 and a secondportion 170. The shaft clutch 166 may be a splined dog type clutch. Theshaft clutch 166 comprises a first toothed portion 172 formed on thefirst portion 168 and a second toothed portion 174 formed on the secondportion 170. The first toothed portion 172 and the second toothedportion 174 may be directed formed on the first portion 168 and thesecond portion 170 or they may be formed on a sleeve located about thefirst portion 168 and the second portion 170. The first toothed portion172 and the second toothed portion 174 respectively rotate with thefirst portion 168 and the second portion 170 of one of the axle halfshafts 162.

The shaft clutch 166 further comprises a locking collar 176 disposedabout one of the axle half shafts 162 and drivingly engaged with atleast one of the first toothed portion 172 and the second toothedportion 174. The locking collar 176 is axially moveable along the firsttoothed portion 172 and the second toothed portion 174 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 176 has a first position and a second position. As shown in FIG.1, the locking collar 176 is in the first position and is drivinglyengaged with the first toothed portion 172. In the second position, thelocking collar 176 is drivingly engaged with the first toothed portion172 and the second toothed portion 174, causing the first portion 168 tobe drivingly engaged with the second portion 170.

The locking collar 176 may be selectively moved along the first toothedportion 172 and the second toothed portion 174 so as to couple the firstportion 168 and the second portion 170. The locking collar 176 may bemoved by an actuator 178 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 178may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The axle half shafts 162 are connected to wheel ends 180. Each wheel end180 supports wheels and tires (not shown).

The shaft clutch 166 permits the second portion 170 to be selectivelydisengaged from the side gear 160, the second axle driving gear 154, thepropeller shaft 142, and thus the first axle assembly 102. As a result,the second axle driving gear 154 and the propeller shaft 142 can idleduring vehicle operation.

The first axle assembly 102 may be utilized for the majority of thevehicle duty cycle requirements. The second axle assembly 104 may beselectively engaged when additional tractive effort is required. Byselectively disengaging and idling the second axle assembly 104 usingthe inter-axle clutch 141, an efficiency over a full time driven firstand second axle assembly is achieved by minimizing axle windage andparasitic drag losses.

The second axle assembly 104 may be selectively and automaticallyengaged by an automated system that comprises wheel speed sensors and acontrol algorithm that eliminates the need for driver control. In such asituation, the second axle assembly 104 can be automatically engaged atvehicle start up to proportion the drive torque between the first andsecond axle assemblies 102, 104. This has the effect of lowering themaximum torque on either the first and second axle assemblies 102, 104.Further, when a friction plate-type clutch is utilized in the inter-axleclutch 141 to engage the second axle assembly 104, as shown in FIG. 1,the clutch torque capacity can be used to limit the torque to the secondaxle assembly 104, thus permitting it to be downsized compared to thefirst axle assembly 102. The present invention also has the advantage ofeliminating an inter-axle differential since the second axle assembly104 is only used under low traction conditions or start up conditions.Also, the inter-axle clutch 141 may be allowed to slip when the driveaxle system 100 negotiates a corner.

Another embodiment of the invention is depicted in FIG. 2. A drive axlesystem 200 comprises a first axle assembly 202 and a second axleassembly 204. The first axle assembly 202 includes a first axle inputshaft 206 with a first end portion 208, a middle portion 210 and asecond end portion 212. The first end portion 208 is connected to asource of rotational power, such as a transmission or engine. One ormore bearings 214 and their associated races may be located about thefirst end portion 208 to facilitate rotation of the first axle inputshaft 206 within a first axle assembly housing 216.

A first drop gear 218 is connected to the middle portion 210 of thefirst axle input shaft 206. The first drop gear 218 may be separatelyformed and splined to the middle portion 210 or it may be unitary withthe middle portion 210, as shown in FIG. 2. The first drop gear 218 ismeshed with a second gear 220.

The second gear 220 may be separately formed and splined to a first endportion 222 of a first axle pinion shaft 224, or the second gear 220 maybe unitary with the first end portion 222 of the first axle pinion shaft224. The first axle pinion shaft 224 may also comprise a middle portion225 and a second end portion 226. The middle portion 225 may besupported by one or more bearings 214 and their associated races topermit the first axle pinion shaft 224 to rotate within the first axleassembly housing 216.

The second end portion 226 of the first axle pinion shaft 224 has afirst pinion gear 228 mounted in a unitary fashion therewith. The firstpinion gear 228 is meshed in a hypoid fashion with a first axle drivinggear 230 to provide rotation to the first axle driving gear 230.

The first axle driving gear 230 may be such as, by way of example only,an 18 inch ring gear, but gears of other sizes are also permissible.

The first axle driving gear 230 is mounted on, or connected, to a firstwheel differential case 232. At least two pinion gears 233 and at leasttwo side gears 234 are located within the first wheel differential case232. As known by those skilled in the art, the pinion gears 233 and theside gears 234 are connected to one another. The side gears 234 are alsoconnected to axle half shafts 235. The axle half shafts 235 extend fromthe first wheel differential case 232 to a wheel end 236. The wheel end236 supports wheels and tires (not shown).

The second end portion 212 of the first axle input shaft 206 has a firstplurality of axially movable discs 238 connected thereto. Each of thediscs 238 may be connected directly to the second end portion 212, asshown in FIG. 2, or they may be located on a sleeve (not shown) locatedabout the second end portion 212.

The first plurality of axially moveable discs 238 is interleaved with asecond plurality of axially moveable discs 240. The second plurality ofaxially moveable discs 240 is located on an interior surface of a clutchbowl 242. The clutch bowl 242 is located radially outward in aconcentric fashion from the first plurality of axially moveable discs238. The second plurality of axially moveable discs 240 is selectivelyaxially movable on the interior surface of the clutch bowl 242. Thesecond end portion 212 or a sleeve, the first plurality of axiallymoveable discs 238, the second plurality of axially moveable discs 240,and the clutch bowl 242 form an inter-axle clutch 244.

The first plurality of axially moveable discs 238 and the secondplurality of axially moveable discs 240 may be selectively compressed soas to couple the clutch bowl 242 and the first axle input shaft 206. Theselective compression is applied by an actuator 246. The actuator 246may be a pneumatic actuator, an electromechanical actuator or ahydraulic actuator. Any of the foregoing may be connected to a vehicleanti-lock braking system to facilitate further vehicle control via thedriveline.

The clutch bowl 242 is connected to a yoke (not shown). The yoke isconnected to a propeller shaft 248, such as through a first universaljoint 250. The propeller shaft 248 is connected to a second universaljoint 252 located on the second axle assembly 204.

The second universal joint 252 is connected to a third pinion shaft 254.A third pinion gear 256 is connected to the third pinion shaft 254. Thethird pinion shaft 254, and thus the third pinion gear 256, is mountedfor rotation within a second wheel differential housing 258. The thirdpinion gear 256 may be such as a spiral bevel, or it may be a hypoid.

The third pinion shaft 254 is connected to a yoke (not shown) at a firstend portion 260. The yoke is connected to the propeller shaft 248, suchas through the second universal joint 252. The propeller shaft 248 isconnected to a second universal joint 252 located on the second axleassembly 204.

The third pinion shaft 254 also has a middle portion 262 and a secondend portion 264. The middle portion 262 may be supported by one or morebearings 214 to facilitate the rotation of the third pinion shaft 254within the second wheel differential housing 258. The second end portion264 of the third pinion shaft 254 comprises the third pinion gear 256.The third pinion gear 256 is drivingly engaged with a second axledriving gear 268. The third pinion gear 256 may be engaged with thesecond axle driving gear 268 in a hypoid type arrangement, but otherembodiments are permissible as well. The third pinion shaft 254 isdrivingly engaged with the second axle driving gear 268 of the secondaxle assembly 204 through a single gear mesh.

As is known in the art and as used herein with respect to each of theembodiments disclosed, the single gear mesh includes driving a secondcomponent with a first component, wherein the first component rotatingabout an axis of the first component drives the second component.Further, it is understood that driving the second component through alocked or substantially non-rotating component is not the single gearmesh. As a first non-limiting example, it is understood that a pinionshaft engaged with a ring gear, wherein a force is applied to the ringgear by the pinion shaft being rotatably driven is the single gear mesh.As a second non-limiting example, it is understood that driving a secondcomponent with a first component using a shift collar is not the singlegear mesh. As a third non-limiting example, it is understood thatdriving a second component with the first component through a lockeddifferential is not the single gear mesh.

The second axle driving gear 268 is mounted on, or connected, to asecond wheel differential case 270. At least two pinion gears 271 and atleast two side gears 272 are located within the second wheeldifferential case 270. As known by those skilled in the art, the piniongears 271 and the side gears 272 are connected to one another. The sidegears 272 are also connected to axle half shafts 274.

The second axle driving gear 268 may have the same or a smaller diameterthan the first axle driving gear 230. By way of example only, the firstaxle driving gear 230 may have a diameter of approximately 18 inches,while the second axle driving gear 268 may have a diameter ofapproximately 14 inches.

A shaft clutch 276 is mounted to one of the axle half shafts 274 anddivides the axle half shaft 274 into a first portion 277 and a secondportion 278. The shaft clutch 276 may be a splined dog type clutch. Theshaft clutch 276 comprises a first toothed portion 280 formed on thefirst portion 277 and a second toothed portion 282 formed on the secondportion 278. The first toothed portion 280 and the second toothedportion 282 may be directed formed on the first portion 277 and thesecond portion 278 or they may be formed on a sleeve located about thefirst portion 277 and the second portion 278. The first toothed portion280 and the second toothed portion 282 respectively rotate with thefirst portion 277 and the second portion 278 of one of the axle halfshafts 274.

The shaft clutch 276 further comprises a locking collar 284 disposedabout one of the axle half shafts 274 and drivingly engaged with atleast one of the first toothed portion 280 and the second toothedportion 282. The locking collar 284 is axially moveable along the firsttoothed portion 280 and the second toothed portion 282 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 284 has a first position and a second position. As shown in FIG.2, the locking collar 284 is in the first position and is drivinglyengaged with the first toothed portion 280. In the second position, thelocking collar 284 is drivingly engaged with the first toothed portion280 and the second toothed portion 282, causing the first portion 277 tobe drivingly engaged with the second portion 278.

The locking collar 284 may be selectively moved along the first toothedportion 280 and the second toothed portion 282 so as to couple the firstportion 277 and the second portion 278. The locking collar 284 may bemoved by an actuator 286 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 286may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The axle half shafts 274 are connected to wheel ends 288. Each wheel end288 supports wheels and tires (not shown).

The shaft clutch 276 permits the second portion 278 to be selectivelydisengaged from the side gear 272, the second axle driving gear 268, thepropeller shaft 248, and thus the first axle assembly 202. As a result,the second axle driving gear 268 and the propeller shaft 248 can idleduring vehicle operation.

The first axle assembly 202 may be utilized for the majority of thevehicle duty cycle requirements. The second axle assembly 204 may beselectively engaged when additional tractive effort is required. Byselectively disengaging and idling the second axle assembly 204 usingthe inter-axle clutch 244, an efficiency over a full time driven firstand second axle assembly is achieved by minimizing axle windage andparasitic drag losses.

The second axle assembly 204 may be selectively and automaticallyengaged by an automated system that comprises wheel speed sensors and acontrol algorithm that eliminates the need for driver control. In such asituation, the second axle assembly 204 can be automatically engaged atvehicle start up to proportion the drive torque between the first andsecond axle assemblies 202, 204. This has the effect of lowering themaximum torque on either the first and second axle assemblies 202, 204.Further, when a friction plate-type clutch is utilized in the inter-axleclutch 244 to engage the second axle assembly 204, as shown in FIG. 2,the clutch torque capacity can be used to limit the torque to the secondaxle assembly 204, thus permitting it to be downsized compared to thefirst axle assembly 202. The present invention also has the advantage ofeliminating an inter-axle differential since the second axle assembly204 is only used under low traction conditions or start up conditions.Also, the inter-axle clutch 244 may be allowed to slip when the driveaxle system 200 negotiates a corner.

Another embodiment of the invention is depicted in FIG. 3. A drive axlesystem 300 comprises a first axle assembly 302 and a second axleassembly 304. The first axle assembly 302 includes a first axle shaft306 with a first end portion 308, a middle portion 310 and a second endportion 312. The first end portion 308 is connected to a source ofrotational power, such as a transmission or engine. One or more bearings314 and their associated races may be located about the first endportion 308 to facilitate rotation of the first axle shaft 306 within afirst axle assembly housing 316.

A clutch bowl 318 is mounted for rotation with the first axle shaft 306,such as through splines. The clutch bowl 318 is located radially outwardfrom, and concentric with, the first axle shaft 306. A first pluralityof axially moveable discs 320 extends radially inward from an innersurface of the clutch bowl 318. The first plurality of axially moveablediscs 320 are interleaved with a second plurality of axially moveablediscs 322 mounted on one end of a drop gear 324. Both pluralities ofaxially moveable discs 320, 322 are moveable in the axial directionalong their respective mounting structures. The second end portion 312or a sleeve, the clutch bowl 318, the first plurality of axiallymoveable discs 320, and the second plurality of axially moveable discs322 form an inter-axle clutch 325.

The first plurality of axially moveable discs 320 and the secondplurality of axially moveable discs 322 may be selectively compressed soas to couple the clutch bowl 318 and the first axle shaft 306. Theselective compression is applied by an actuator 326. The actuator 326may be a pneumatic actuator, an electromechanical actuator or ahydraulic actuator. Any of the foregoing may be connected to a vehicleanti-lock braking system to facilitate further vehicle control via thedriveline.

The drop gear 324 has a set of radially extending teeth. The teeth ofthe drop gear 324 engage with a plurality of teeth formed on a secondgear 327 fixed to a pinion shaft 328. The pinion shaft 328 has a firstpinion gear 329 fixed thereto which engages a first axle driving gear330. The first pinion gear 329 may be engaged with the first axledriving gear 330 in a hypoid type arrangement, but other embodiments arepermissible as well.

The first axle driving gear 330 is mounted on, or connected, to a firstwheel differential case 332. At least two pinion gears 333 and at leasttwo side gears 334 are located within the first wheel differential case332. As known by those skilled in the art, the pinion gears 333 and theside gears 334 are connected to one another. The side gears 334 are alsoconnected to axle half shafts 335.

A shaft clutch 338 is mounted to one of the axle half shafts 335 anddivides the axle half shaft 335 into a first portion 340 and a secondportion 341. The shaft clutch 338 may be a splined dog type clutch. Theshaft clutch 338 comprises a first toothed portion 342 formed on thefirst portion 340 and a second toothed portion 343 formed on the secondportion 341. The first toothed portion 342 and the second toothedportion 343 may be directed formed on the first portion 340 and thesecond portion 341 or they may be formed on a sleeve located about thefirst portion 340 and the second portion 341. The first toothed portion342 and the second toothed portion 343 respectively rotate with thefirst portion 340 and the second portion 341 of one of the axle halfshafts 335.

The shaft clutch 338 further comprises a locking collar 344 disposedabout one of the axle half shafts 335 and drivingly engaged with atleast one of the first toothed portion 342 and the second toothedportion 343. The locking collar 344 is axially moveable along the firsttoothed portion 342 and the second toothed portion 343 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 344 has a first position and a second position. As shown in FIG.3, the locking collar 344 is in the first position and is drivinglyengaged with the first toothed portion 342. In the second position, thelocking collar 344 is drivingly engaged with the first toothed portion342 and the second toothed portion 343, causing the first portion 340 tobe drivingly engaged with the second portion 341.

The locking collar 344 may be selectively moved along the first toothedportion 342 and the second toothed portion 343 so as to couple the firstportion 340 and the second portion 341. The locking collar 344 may bemoved by an actuator 346 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 346may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The axle half shafts 335 are connected to wheel ends 336. Each wheel end336 supports wheels and tires (not shown).

The shaft clutch 338 permits the second portion 341 to be selectivelydisengaged from the side gear 334, the first axle driving gear 330, thepinion shaft 328, the drop gear 324, and thus the first axle shaft 306.As a result, the first axle driving gear 330 and the pinion shaft 328can idle during vehicle operation.

The second end portion 312 of the first axle shaft 306 is supported byone or more bearings 314 and their associated races for rotation withinthe first axle assembly housing 316. The second end portion 312 of thefirst axle shaft 306 is connected to a yoke (not shown). The yoke isconnected to a propeller shaft 348, such as through a first universaljoint 350. The propeller shaft 348 is connected to a second universaljoint 352 located on the second axle assembly 304.

The second universal joint 352 is connected to a second pinion shaft354. A second pinion gear 356 is connected to the second pinion shaft354. The second pinion shaft 354, and thus the second pinion gear 356,is mounted for rotation within a second wheel differential housing 358.The second pinion gear 356 may be such as a spiral bevel, or it may be ahypoid.

The second pinion shaft 354 is connected to a yoke (not shown) at afirst end portion 360. The yoke is connected to the propeller shaft 348,such as through the second universal joint 352. The propeller shaft 348is connected to a second universal joint 352 located on the second axleassembly 304.

The second pinion shaft 354 also has a middle portion 362 and a secondend portion 364. The middle portion 362 may be supported by one or morebearings 314 to facilitate the rotation of the second pinion shaft 354within the second wheel differential housing 358. The second pinion gear356 is drivingly engaged with a second axle driving gear 368. The secondpinion gear 356 may be engaged with the second axle driving gear 368 ina hypoid type arrangement, but other embodiments are permissible aswell. The second pinion shaft 354 is drivingly engaged with the secondaxle driving gear 368 of the second axle assembly 304 through a singlegear mesh.

The second axle driving gear 368 is mounted on, or connected, to asecond wheel differential case 370. At least two pinion gears 371 and atleast two side gears 372 are located within the second wheeldifferential case 370. As known by those skilled in the art, the piniongears 371 and the side gears 372 are connected to one another. The sidegears 372 are also connected to axle half shafts 374.

The second axle driving gear 368 may have the same or a greater diameterthan the first axle driving gear 330. By way of example only, the firstaxle driving gear 330 may have a diameter of approximately 14 inches,while the second axle driving gear 368 may have a diameter ofapproximately 18 inches.

The second axle assembly 304 may be utilized for the majority of thevehicle duty cycle requirements. The first axle assembly 302 may beselectively engaged when additional tractive effort is required. Byselectively disengaging and idling the second axle assembly 304 usingthe inter-axle clutch 325, an efficiency over a full time driven firstand second axle assembly is achieved by minimizing axle windage andparasitic drag losses.

The first axle assembly 302 may be selectively and automatically engagedby an automated system that comprises wheel speed sensors and a controlalgorithm that eliminates the need for driver control. In such asituation, the first axle assembly 302 can be automatically engaged atvehicle start up to proportion the drive torque between the first andsecond axle assemblies 302, 304. This has the effect of lowering themaximum torque on either the first and second axle assemblies 302, 304.Further, when a friction plate-type clutch is utilized in the inter-axleclutch 325 to engage the first axle assembly 302, as shown in FIG. 3,the clutch torque capacity can be used to limit the torque to the firstaxle assembly 302, thus permitting it to be downsized compared to thesecond axle assembly 304. The present invention also has the advantageof eliminating an inter-axle differential since the first axle assembly302 is only used under low traction conditions or start up conditions.Also, the inter-axle clutch 325 may be allowed to slip when the driveaxle system 300 negotiates a corner.

Another embodiment of the invention is depicted in FIG. 4. A drive axlesystem 400 comprises a first axle assembly 402 and a second axleassembly 404. The first axle assembly 402 includes a first axle inputshaft 406 with a first end portion 408, a middle portion 410 and asecond end portion 412. The first end portion 408 is connected to asource of rotational power, such as a transmission or engine. One ormore bearings 414 and their associated races may be located about thefirst end portion 408 to facilitate rotation of the first axle inputshaft 406 within a first axle assembly housing 416.

A clutch bowl 418 is mounted concentrically about and radially outwardfrom the first axle input shaft 406. One or more bearings 414 and theirassociated races may be located about a portion of the clutch bowl 418to facilitate rotation of the clutch bowl 418 within the first axleassembly housing 416. A first plurality of axially moveable discs 420extends radially inward from an inner surface of the clutch bowl 418.The first plurality of axially moveable discs 420 are interleaved with asecond plurality of axially moveable discs 422 mounted on the first axleinput shaft 406. As shown in FIG. 4, the first plurality of axiallymoveable discs 420 comprises three discs and the second plurality ofaxially moveable discs 422 comprises two discs; however, it isunderstood the first plurality of axially moveable discs 420 and thesecond plurality of axially moveable discs 422 may comprise any numberof discs. Both pluralities of axially moveable discs 420, 422 aremoveable in the axial direction along their respective mountingstructures. A plurality of teeth formed in an outer surface of theclutch bowl 418 or a gear fixed to the outer surface of the clutch bowlforms a drop gear 424. The clutch bowl 418, the first plurality ofaxially moveable discs 420, and the second plurality of axially moveablediscs 422 form an inter-axle clutch 425.

The first plurality of axially moveable discs 420 and the secondplurality of axially moveable discs 422 may be selectively compressed soas to couple the clutch bowl 418 and the first axle input shaft 406. Theselective compression is applied by an actuator 426. The actuator 426may be a pneumatic actuator, an electromechanical actuator or ahydraulic actuator. Any of the foregoing may be connected to a vehicleanti-lock braking system to facilitate further vehicle control via thedriveline.

The drop gear 424 has a set of radially extending teeth. The teeth ofthe drop gear 424 engage with a plurality of teeth formed on a secondgear 427 fixed to a first end 428 of an output shaft 429. One or morebearings 414 and their associated races may be located about a portionof the output shaft 429 to facilitate rotation of the clutch outputshaft 429 within the first axle assembly housing 416.

The first axle input shaft 406 has a first pinion gear 430 fixed theretowhich engages a first axle driving gear 431. The first pinion gear 430may be engaged with the first axle driving gear 431 in a hypoid typearrangement, but other embodiments are permissible as well. The firstaxle input shaft 406 is drivingly engaged with the first axle drivinggear 431 of the first axle assembly 402 through a single gear mesh.

The first axle driving gear 431 is mounted on, or connected, to an outercase portion 432 of an axle ratio selection device 433. The axle ratioselection device 433 includes an inner case portion 434, the outer caseportion 432, a plurality of case pinions 435, and a ratio selector 436.As is known in the art, the axle ratio selection device 433 comprises aplanetary gear set; however, it is understood that the axle ratioselection device 433 may be any other type of multi speed selectiondevice. The outer case portion 432 has a toothed case end 437. The innercase portion 434 is rotatably and concentrically mounted within theouter case portion 432. The plurality of case pinions 435 are rotatablymounted to an end of the inner case portion 434 and engage a case ringgear 438 formed on an inner surface of the outer case portion 432.

The ratio selector 436 is a hollow member disposed about one of a pairof axle half shafts 439. One or more bearings (not shown) and theirassociated races may be located about a portion of the ratio selector436 to facilitate rotation of the ratio selector 436 within the firstaxle assembly housing 416.

The ratio selector 436 has a first toothed end 440 and a second toothedend 441 and may be placed in a first position or a second position alongthe case pinion 435. In the first position, the first toothed end 440 ofthe ratio selector 436 engages the toothed case end 437 and the casepinions 435, “locking out” the planetary gear set of the axle ratioselection device 433. When the ratio selector 436 is placed in the firstposition, the case ring gear 438, the ratio selector 436, and the casepinions 435 (and thus the inner case portion 434), are driven at a sameangular velocity.

In the second position, the first toothed end 440 of the ratio selector436 engages the case pinions 435 and the second toothed end 441 of theratio selector 436 engages a toothed portion of the first axle assemblyhousing 416, fixing the first toothed end 440 with respect to the firstaxle assembly housing 416. When the ratio selector 436 is placed in thesecond position, the case ring gear 438 drives the case pinions 435, andthus the inner case portion 434, about the first toothed end 440 at areduced ratio when compared to the ratio selector 436 placed in thefirst position.

The ratio selector 436 may be moved by an actuator 442 such as apneumatic actuator, an electromechanical actuator, or a hydraulicactuator. The actuator 442 may be connected to the anti-lock brakingsystem of the vehicle, as described below.

At least two pinion gears 443 and at least two side gears 444 arelocated within the inner case portion 434. As known by those skilled inthe art, the pinion gears 443 and the side gears 444 are connected toone another. The side gears 443 are also connected to the axle halfshafts 439.

The axle half shafts 439 are connected to wheel ends 446. Each wheel end446 supports wheels and tires (not shown).

A second end 448 of the output shaft 429 is supported by one or morebearings 414 and their associated races for rotation within the firstaxle assembly housing 416. The second end 448 of the output shaft 429 isconnected to a yoke (not shown). The yoke is connected to a propellershaft 450, such as through a first universal joint 452. The propellershaft 450 is connected to a second universal joint 454 located on thesecond axle assembly 404.

The second universal joint 454 is connected to a second pinion shaft456. A second pinion gear 458 is connected to the second pinion shaft456. The second pinion shaft 456, and thus the second pinion gear 458,is mounted for rotation within a second wheel differential housing 460.The second pinion gear 458 may be such as a spiral bevel, or it may be ahypoid. The second pinion shaft 456 is connected to a yoke (not shown)at a first end portion 462. The yoke is connected to the propeller shaft450, such as through the second universal joint 454. The propeller shaft450 is connected to a second universal joint 454 located on the secondaxle assembly 404.

The second pinion shaft 456 also has a middle portion 464 and a secondend portion 466. The middle portion 464 may be supported by one or morebearings 414 to facilitate the rotation of the second pinion shaft 456within the second wheel differential housing 460. The second pinion gear458 is drivingly engaged with a second axle driving gear 468. The secondpinion gear 458 may be engaged with the second axle driving gear 468 ina hypoid type arrangement, but other embodiments are permissible aswell.

The second axle driving gear 468 is mounted on, or connected, to asecond wheel differential case 470. At least two pinion gears 471 and atleast two side gears 472 are located within the second wheeldifferential case 470. As known by those skilled in the art, the piniongears 471 and the side gears 472 are connected to one another. The sidegears 472 are also connected to axle half shafts 474. The second axledriving gear 468 may have the same or a different diameter than thefirst axle driving gear 431.

A shaft clutch 476 is mounted to one of the axle half shafts 474 anddivides the axle half shaft 474 into a first portion 477 and a secondportion 478. The shaft clutch 476 may be a splined dog type clutch. Theshaft clutch 476 comprises a first toothed portion 480 formed on thefirst portion 477 and a second toothed portion 482 formed on the secondportion 478. The first toothed portion 480 and the second toothedportion 482 may be directed formed on the first portion 477 and thesecond portion 478 or they may be formed on a sleeve located about thefirst portion 477 and the second portion 478. The first toothed portion480 and the second toothed portion 482 respectively rotate with thefirst portion 477 and the second portion 478 of one of the axle halfshafts 474.

The shaft clutch 476 further comprises a locking collar 484 disposedabout one of the axle half shafts 474 and drivingly engaged with atleast one of the first toothed portion 480 and the second toothedportion 482. The locking collar 484 is axially moveable along the firsttoothed portion 480 and the second toothed portion 482 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 484 has a first position and a second position. As shown in FIG.4, the locking collar 484 is in the first position and is drivinglyengaged with the first toothed portion 480. In the second position, thelocking collar 484 is drivingly engaged with the first toothed portion480 and the second toothed portion 482, causing the first portion 477 tobe drivingly engaged with the second portion 478.

The locking collar 484 may be selectively moved along the first toothedportion 480 and the second toothed portion 482 so as to couple the firstportion 477 and the second portion 478. The locking collar 484 may bemoved by an actuator 486 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 486may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The shaft clutch 476 permits the second portion 478 to be selectivelydisengaged from the side gear 472, the second axle driving gear 468, thesecond pinion shaft 456, the propeller shaft 450, and thus the outputshaft 429. As a result, the second axle driving gear 468, the secondpinion shaft 456, the propeller shaft 450, and the output shaft 429 canidle during vehicle operation.

The first axle assembly 402 may be utilized for the majority of thevehicle duty cycle requirements. The ratio selector 436 of the axleratio selection device 433 in the first position results in a gear ratioof the first axle assembly 402 selected for a high speed and low torquemanner of operation. The gear ratio of the first axle assembly 402having the axle ratio selection device 433 in the first positionpreferably is employed during a single axle mode of operation, where thehigh speed and low torque manner of operation is desired. The ratioselector 436 of the axle ratio selection device 433 in the secondposition results in a gear ratio of the first axle assembly 402 selectedfor a low speed and high torque manner of operation. The gear ratio ofthe first axle assembly 402 having the axle ratio selection device 433in the second position preferably corresponds to a gear ratio of thesecond axle assembly 404 and is employed during a multi-axle mode ofoperation, where the low speed and high torque manner of operation isdesired.

The second axle assembly 404 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thesecond axle assembly 404 using the inter-axle clutch 425, an efficiencyover a full time driven first and second axle assembly 402, 404 isachieved by minimizing axle windage and parasitic drag losses.

The second axle assembly 404 may be selectively and automaticallyengaged by an automated system that comprises wheel speed sensors and acontrol algorithm that eliminates the need for driver control. In such asituation, the second axle assembly 404 can be automatically engaged atvehicle start up to proportion the drive torque between the first andsecond axle assemblies 402, 404. This has the effect of lowering themaximum torque on either the first and second axle assemblies 402, 404.Further, when a friction plate-type clutch is utilized in the inter-axleclutch 425 to engage the second axle assembly 404, as shown in FIG. 4,the clutch torque capacity can be used to limit the torque to the secondaxle assembly 404, thus permitting it to be downsized compared to thefirst axle assembly 402. The present invention also has the advantage ofeliminating an inter-axle differential since the second axle assembly404 is only used under low traction conditions or start up conditions.Also, the inter-axle clutch 425 may be allowed to slip when the driveaxle system 400 negotiates a corner.

FIG. 5 depicts yet another embodiment of the present invention. FIG. 5depicts a drive axle system 500 comprised of a first axle assembly 502and a second axle assembly 504. The first axle assembly 502 includes afirst axle input shaft 506 with a first end portion 508, a middleportion 510 and a second end portion 512. The first end portion 508 isconnected to a source of rotational power, such as a transmission or anengine. One or more bearings 514 and their associated races may belocated about the first end portion 508 to facilitate rotation of thefirst axle input shaft 506 within a first axle assembly housing 516.

The middle portion 510 may have a set of splines (not shown) locatedcircumferentially about an outer surface of the first axle input shaft506. A spider 518 having an inner diameter with a complimentary set ofsplines is located over the set of splines formed on the first axleinput shaft 506. The spider 518 is thus rotatably connected with thefirst axle input shaft 506.

The spider 518 extends radially outward circumferentially from the firstaxle input shaft 506. The spider 518 is part of an inter-axledifferential 520 which also comprises a plurality of pinion gears 522.Each of the pinion gears 522 may be a bevel type pinion gear. At leasttwo pinion gears 522 are located on the spider 518, and more may beused. The spider 518 may extend through an aperture formed in each ofthe pinion gears 522.

The pinion gears 522 engage on one side with a first drop gear 524 and asecond axle side gear 525 on an opposing side. The pinion gears 522apply a rotational force to side gear teeth formed on the first dropgear 524 as well as side gear teeth formed on the second axle side gear525.

The second axle side gear 525, in addition to the side gear teeth formedthereon, includes of a first set of clutch teeth 526 formed thereon.

The first drop gear 524 is concentric with the middle portion 510 of thefirst axle input shaft 506. In addition to the side gear teeth formedthereon, a set of drop gear teeth are located on the radiallyoutward-most point of the first drop gear 524. The first drive gearteeth are meshed with another set of teeth of a second drop gear 527.

The second drop gear 527 is concentric with a first pinion shaft 528located below the first axle input shaft 506. The second drop gear 527may have a splined inner surface that engages with a splined outersurface of the first pinion shaft 528. The second drop gear 527 islocated on a first end portion 529 of the first pinion shaft 528.

The first pinion shaft 528 also has a middle portion 530 and a secondend portion 531. The middle portion 530 may be supported for rotationwithin the first axle assembly housing 516 by one or more bearings 514and their associated races. The second end portion 531 includes a firstpinion gear 532 disposed thereon.

The first pinion gear 532 is located in driving engagement with a firstaxle driving gear 533, such as in a hypoid orientation. Otherorientations of the first axle driving gear 533 and the first piniongear 532 are also permissible.

The first axle driving gear 533 is mounted on, or connected, to a firstwheel differential case 534. At least two pinion gears 535 and at leasttwo side gears 536 are located within the first wheel differential case534. As known by those skilled in the art, the pinion gears 535 and theside gears 536 are connected to one another. The side gears 536 are alsoconnected to axle half shafts 537.

A shaft clutch 538 is mounted to one of the axle half shafts 537 anddivides the axle half shaft 537 into a first portion 540 and a secondportion 541. The shaft clutch 538 may be a splined dog type clutch. Theshaft clutch 538 comprises a first toothed portion 542 formed on thefirst portion 540 and a second toothed portion 543 formed on the secondportion 541. The first toothed portion 542 and the second toothedportion 543 may be directed formed on the first portion 540 and thesecond portion 541 or they may be formed on a sleeve located about thefirst portion 540 and the second portion 541. The first toothed portion542 and the second toothed portion 543 respectively rotate with thefirst portion 540 and the second portion 541 of one of the axle halfshafts 537.

The shaft clutch 538 further comprises a locking collar 544 disposedabout one of the axle half shafts 537 and drivingly engaged with atleast one of the first toothed portion 542 and the second toothedportion 543. The locking collar 544 is axially moveable along the firsttoothed portion 542 and the second toothed portion 543 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 544 has a first position and a second position. As shown in FIG.5, the locking collar 544 is in the first position and is drivinglyengaged with the first toothed portion 542. In the second position, thelocking collar 544 is drivingly engaged with the first toothed portion542 and the second toothed portion 543, causing the first portion 540 tobe drivingly engaged with the second portion 541.

The locking collar 544 may be selectively moved along the first toothedportion 542 and the second toothed portion 543 so as to couple the firstportion 540 and the second portion 541. The locking collar 544 may bemoved by an actuator 546 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 546may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The axle half shafts 537 are connected to wheel ends 547. Each wheel end547 supports wheels and tires (not shown).

The shaft clutch 538 permits the second portion 541 to be selectivelydisengaged from the side gear 536, the first axle driving gear 533, thefirst pinion shaft 528, the second drop gear 527, and thus the firstdrop gear 524. As a result, the first axle driving gear 533 and thefirst pinion shaft 528 can idle during vehicle operation.

The first axle input shaft 506 is provided with a set of teeth formed onthe second end portion 512 for engaging an output shaft clutch collar548. Preferably, the teeth formed on the second end portion 512 areunitary with the first axle input shaft 506. However, it is permissiblefor the teeth to be located on a collar that is splined to the firstaxle input shaft 506. The teeth formed on the second end portion 512 arelocated axially adjacent a set of clutch teeth formed on the second axleside gear 525.

The output shaft clutch collar 548 is located radially outward from andconcentric with at least a portion of the first axle input shaft 506.The output shaft clutch collar 548 may be connected to an actuator 550,such as a shift fork, for selectively moving the output shaft clutchcollar 548 in an axial direction. The output shaft clutch collar 548 mayhave a circumferential groove located in an outer surface thereof. Theshift fork may engage with all or a portion of the circumferentialgroove to move the output shaft clutch collar 548 in the axialdirection.

The output shaft clutch collar 548 has an inner surface with a first setof teeth and a second set of teeth formed thereon. The first set ofteeth may be located on a front portion of the inner surface of theoutput shaft clutch collar 548 while the second set of teeth are locatedon an rear side of the inner surface of the output shaft clutch collar548.

The first set of teeth formed on the inner surface of the output shaftclutch collar 548 may selectively engage with either the set of teethformed on the second end portion 512 of the first axle input shaft 506or the set of clutch teeth formed on the second axle side gear 525. Thesecond set of teeth formed on the inner surface of the output shaftclutch collar 548 is always engaged with a set of teeth on an outersurface of an output shaft 552. The set of teeth on the outer surface ofthe output shaft 552 have a predetermined axial length. The length ofteeth formed on the output shaft 552 is sufficient to permit the secondset of teeth formed on the output shaft clutch collar 548 to always beengaged therewith regardless of the axial position of the output shaftclutch collar 548.

The output shaft 552 comprises a first end portion 554, a middle portion556, and a second end portion 558. The set of teeth on the outer surfaceof the output shaft 552 are formed on the first end portion 554. Thefirst end portion 554 may also define an inner axial cavity 560 designedto receive at least a portion of the second end portion 512 of the firstaxle input shaft 506 therein.

The middle portion 556 of the output shaft 552 may be supported by oneor more bearings 514 and their associated races. The bearings 514facilitate rotation of the output shaft 552 within the first axleassembly housing 516.

The second end portion 558 comprises a yoke (not shown) for connectingwith a first universal joint 566. The first universal joint 566 isconnected to a propeller shaft 564. The propeller shaft 564 extendsbetween the first axle assembly 502 and the second axle assembly 504.

A second universal joint 566 is connected to a second pinion shaft 568.A second pinion gear 570 is connected to the second pinion shaft 568.The second pinion shaft 568, and thus the second pinion gear 570, ismounted for rotation within a second wheel differential housing 571. Thesecond pinion gear 570 may be such as a spiral bevel, or it may be ahypoid.

The second pinion shaft 568 is connected to a yoke (not shown) at afirst end portion 572. The yoke is connected to the propeller shaft 564,such as through the second universal joint 566.

The second pinion shaft 568 also has a middle portion 574 and a secondend portion 576. The middle portion 574 may be supported by one or morebearings 514 to facilitate the rotation of the second pinion shaft 568within the second wheel differential housing 571. The second pinion gear570 is drivingly engaged with a second axle driving gear 577. The secondpinion gear 570 may be engaged with the second axle driving gear 577 ina hypoid type arrangement, but other embodiments are permissible aswell. The second pinion shaft 568 is drivingly engaged with the secondaxle driving gear 577 of the second axle assembly 504 through a singlegear mesh.

The second axle driving gear 577 is mounted on, or connected, to asecond wheel differential case 578. At least two pinion gears 580 and atleast two side gears 582 are located within the second wheeldifferential case 578. As known by those skilled in the art, the piniongears 580 and the side gears 582 are connected to one another. The sidegears 582 are also connected to axle half shafts 584.

The second axle driving gear 577 may have the same or a greater diameterthan the first axle driving gear 533. By way of example only, the firstaxle driving gear 533 may have a diameter of approximately 14 inches,while the second axle driving gear 577 may have a diameter ofapproximately 18 inches.

The drive axle system 500 may be placed in a first mode of operation anda second mode of operation. In the first mode of operation, the firstaxle assembly 502 is disengaged and the second axle assembly 504 isengaged. In the second mode of operation, the first axle assembly 502and the second axle assembly 504 is engaged and driven through theinter-axle differential 520.

To place the drive axle system 500 in the first mode of operation, theoutput shaft clutch collar 548 is placed in driving engagement with thefirst axle input shaft 506 and the output shaft 552. Further, thelocking collar 544 of the shaft clutch 538 is placed in the firstposition. When the output shaft clutch collar 548 is placed in drivingengagement with the first axle input shaft 506 and the output shaft 552,the spider 518 is driven, causing the second axle side gear 525 torotate about the first axle input shaft 506 in a non-driving manner.Because the locking collar 544 of the shaft clutch 538 is placed in thefirst position, the first axle driving gear 533, the first pinion shaft528, the second drop gear 527, and the first drop gear 524 are drivinglydisengaged from the axle half shafts 537, allowing the first axledriving gear 533, the first pinion shaft 528, the second drop gear 527,and the first drop gear 524 to remain in a non-moving state when thedrive axle system 500 is placed in the first mode of operation. Thedrive axle system 500 placed in the first mode of operation is employedwhere a single axle drive and a high speed and low torque manner ofoperation is desired.

To place the drive axle system 500 in the second mode of operation, theoutput shaft clutch collar 548 is placed in driving engagement with thefirst set of clutch teeth 526 formed on the second axle side gear 525and the output shaft 552. Further, the locking collar 544 of the shaftclutch 538 is placed in the second position. When the output shaftclutch collar 548 is placed in driving engagement with the second axleside gear 525 and the output shaft 552, the spider 518 drivingly engagesboth the second axle side gear 525 and the first drop gear 524. Becausethe locking collar 544 of the shaft clutch 538 is placed in the secondposition, the first axle driving gear 533 drivingly engages the axlehalf shafts 537. The drive axle system 500 placed in the second mode ofoperation is employed where a multi-axle drive and a low speed and hightorque manner of operation is desired.

The first axle assembly 502 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thefirst axle assembly 502 using the output shaft clutch collar 548, anefficiency over a full time driven first and second axle assembly 502,504 is achieved by minimizing axle windage and parasitic drag losses.

The first axle assembly 502 may be selectively and automatically engagedby an automated system that comprises wheel speed sensors and a controlalgorithm that eliminates the need for driver control. In such asituation, the first axle assembly 502 can be automatically engaged atvehicle start up or when the vehicle is in a substantially non-movingstate to proportion the drive torque between the first and second axleassemblies 502, 504. This has the effect of lowering the maximum torqueon either the first and second axle assemblies 502, 504.

FIG. 6 depicts yet another embodiment of the present invention. FIG. 6depicts a drive axle system 600 comprised of a first axle assembly 602and a second axle assembly 604.

The first axle assembly 602 includes a first axle input shaft 606 with afirst end portion 608, a middle portion 610 and a second end portion612. The first end portion 608 is connected to a source of rotationalpower, such as a transmission or an engine. A first engagement portion613 including a set of clutch teeth extends radially from the first axleinput shaft 606 adjacent the first end portion 608. One or more bearings614 and their associated races may be located about the first endportion 608 to facilitate rotation of the first axle input shaft 606within a first axle assembly housing 616.

A spider shaft 618 is rotatably disposed about the first axle inputshaft 606. One or more bearings (not shown) and their associated racesmay be located about the first axle input shaft 606 or the spider shaft618 to facilitate rotation of the first axle input shaft 606 within thefirst axle assembly housing 616. The spider shaft 618 includes a pinionend 619 and a spider engagement end 620.

The pinion end 619 extends radially outward circumferentially from thefirst axle input shaft 606. The pinion end is part of an inter-axledifferential 621 which also comprises a plurality of pinion gears 622.Each of the pinion gears 622 may be a bevel type pinion gear. At leasttwo pinion gears 622 are located on the pinion end 619, and more may beused. The pinion end 619 may extend through an aperture formed in eachof the pinion gears 622.

The spider engagement end 620 extends radially outward circumferentiallyfrom the first axle input shaft 606 opposite the pinion end 619 of thespider shaft 618. The spider engagement end 620 is positioned adjacentthe first engagement portion 613 of the first axle input shaft 606. Thespider engagement end 620 includes a set of clutch teeth formed thereon.

The pinion gears 622 engage on one side with a first drop gear 623 and asecond axle side gear 624 on an opposing side. The pinion gears 622apply a rotational force to side gear teeth formed on the first dropgear 623 as well as side gear teeth formed on the second axle side gear624.

The second axle side gear 624, in addition to the side gear teeth formedthereon, includes of a set of clutch teeth formed thereon. One or morebearings (not shown) and their associated races may be located about thesecond axle side gear 624 to facilitate rotation of the second axle sidegear 624 within the first axle assembly housing 616.

The first drop gear 623 is concentric with the first axle input shaft506 and the spider shaft 618. In addition to the side gear teeth formedthereon, a set of drop gear teeth are located on the radiallyoutward-most point of the first drop gear 623. The first drive gearteeth are meshed with another set of teeth of a second drop gear 625.

The second drop gear 625 is concentric with a first pinion shaft 626located below the first axle input shaft 606. The second drop gear 625may have a splined inner surface that engages with a splined outersurface of the first pinion shaft 626. The second drop gear 625 islocated on a first end portion 627 of the first pinion shaft 626.

The first pinion shaft 626 also has a middle portion 628 and a secondend portion 629. The middle portion 628 may be supported for rotationwithin the first axle assembly housing 616 by one or more bearings 614and their associated races. The second end portion 629 includes a firstpinion gear 630 disposed thereon.

The first pinion gear 630 is located in driving engagement with a firstaxle driving gear 631, such as in a hypoid orientation. Otherorientations of the first axle driving gear 631 and the first piniongear 630 are also permissible.

The first axle driving gear 631 is mounted on, or connected, to a firstwheel differential case 632. At least two pinion gears 633 and at leasttwo side gears 634 are located within the first wheel differential case632. As known by those skilled in the art, the pinion gears 633 and theside gears 634 are connected to one another. The side gears 634 are alsoconnected to axle half shafts 635.

A shaft clutch 636 is mounted to one of the axle half shafts 635 anddivides the axle half shaft 635 into a first portion 638 and a secondportion 639. The shaft clutch 636 may be a splined dog type clutch. Theshaft clutch 636 comprises a first toothed portion 640 formed on thefirst portion 638 and a second toothed portion 641 formed on the secondportion 639. The first toothed portion 640 and the second toothedportion 641 may be directed formed on the first portion 638 and thesecond portion 639 or they may be formed on a sleeve located about thefirst portion 638 and the second portion 639. The first toothed portion640 and the second toothed portion 641 respectively rotate with thefirst portion 638 and the second portion 639 of one of the axle halfshafts 635.

The shaft clutch 636 further comprises a locking collar 642 disposedabout one of the axle half shafts 635 and drivingly engaged with atleast one of the first toothed portion 640 and the second toothedportion 641. The locking collar 642 is axially moveable along the firsttoothed portion 640 and the second toothed portion 641 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 642 has a first position and a second position. As shown in FIG.6, the locking collar 642 is in the first position and is drivinglyengaged with the first toothed portion 640. In the second position, thelocking collar 642 is drivingly engaged with the first toothed portion640 and the second toothed portion 641, causing the first portion 638 tobe drivingly engaged with the second portion 639.

The locking collar 642 may be selectively moved along the first toothedportion 640 and the second toothed portion 641 so as to couple the firstportion 638 and the second portion 639. The locking collar 642 may bemoved by an actuator 643 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 643may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The axle half shafts 635 are connected to wheel ends 644. Each wheel end644 supports wheels and tires (not shown).

The shaft clutch 636 permits the second portion 639 to be selectivelydisengaged from the side gear 634, the first axle driving gear 631, thefirst pinion shaft 626, the second drop gear 625, and thus the firstdrop gear 623. As a result, the first axle driving gear 631 and thefirst pinion shaft 626 can idle during vehicle operation.

The first axle input shaft 606 is provided with a set of teeth formed onthe second end portion 612 for engaging an output shaft clutch collar645. Preferably, the teeth formed on the second end portion 612 areunitary with the first axle input shaft 606. However, it is permissiblefor the teeth to be located on a collar that is splined to the firstaxle input shaft 606. The teeth formed on the second end portion 612 arelocated axially adjacent a set of clutch teeth formed on the second axleside gear 624.

The output shaft clutch collar 645 is located radially outward from andconcentric with at least a portion of the first axle input shaft 606.The output shaft clutch collar 645 may be connected to an actuator 646,such as a shift fork, for selectively moving the output shaft clutchcollar 645 in an axial direction. The output shaft clutch collar 645 mayhave a circumferential groove located in an outer surface thereof. Theshift fork may engage with all or a portion of the circumferentialgroove to move the output shaft clutch collar 645 in the axialdirection.

The output shaft clutch collar 645 has an inner surface with a first setof teeth and a second set of teeth formed thereon. The first set ofteeth may be located on a front portion of the inner surface of theoutput shaft clutch collar 645 while the second set of teeth are locatedon an rear side of the inner surface of the output shaft clutch collar645.

The first set of teeth formed on the inner surface of the output shaftclutch collar 645 may selectively engage with either the set of teethformed on the second end portion 612 of the first axle input shaft 606or the set of clutch teeth formed on the second axle side gear 624. Thesecond set of teeth formed on the inner surface of the output shaftclutch collar 645 is always engaged with a set of teeth on an outersurface of an output shaft 647. The set of teeth on the outer surface ofthe output shaft 647 have a predetermined axial length. The length ofteeth formed on the output shaft 647 is sufficient to permit the secondset of teeth formed on the output shaft clutch collar 645 to always beengaged therewith regardless of the axial position of the output shaftclutch collar 645.

The output shaft 647 comprises a first end portion 648, a middle portion649, and a second end portion 650. The set of teeth on the outer surfaceof the output shaft 647 are formed on the first end portion 648. Thefirst end portion 648 may also define an inner axial cavity 651 designedto receive at least a portion of the second end portion 612 of the firstaxle input shaft 606 therein.

The middle portion 649 of the output shaft 647 may be supported by oneor more bearings 614 and their associated races. The bearings 614facilitate rotation of the output shaft 647 within the first axleassembly housing 616.

The second end portion 650 comprises a yoke (not shown) for connectingwith a first universal joint 652. The first universal joint 652 isconnected to a propeller shaft 653. The propeller shaft 653 extendsbetween the first axle assembly 602 and the second axle assembly 604.

The set of clutch teeth formed on the first engagement portion 613 ofthe first axle input shaft 606 engage a spider shaft clutch collar 654.Preferably, set of clutch teeth formed on the first engagement portion613 are unitary with the first axle input shaft 606. However, it ispermissible for the teeth to be located on a collar that is splined tothe first axle input shaft 606. The set of clutch teeth formed on thefirst engagement portion 613 are located axially adjacent the set ofclutch teeth formed on the spider engagement end 620 of the spider shaft618.

The spider shaft clutch collar 654 is located radially outward from andconcentric with at least a portion of the first axle input shaft 606.The spider shaft clutch collar 654 may be connected to an actuator 656,such as a shift fork, for selectively moving the spider shaft clutchcollar 654 in an axial direction. The spider shaft clutch collar 654 mayhave a circumferential groove located in an outer surface thereof. Theshift fork may engage with all or a portion of the circumferentialgroove to move the spider shaft clutch collar 654 in the axialdirection.

The spider shaft clutch collar 654 has an inner surface with a set ofteeth formed thereon. The set of teeth formed on the inner surface ofthe spider shaft clutch collar 654 is always engaged with the set ofclutch teeth formed on the first engagement portion 613. The set ofclutch teeth formed on the first engagement portion 613 have apredetermined axial length. The length of the set of clutch teeth formedon the first engagement portion 613 is sufficient to permit the set ofteeth formed on the spider shaft clutch collar 654 to always be engagedtherewith regardless of the axial position of the spider shaft clutchcollar 654. The set of teeth formed on the inner surface of the spidershaft clutch collar 654 may selectively engage the set of clutch teethformed on the spider engagement end 620 of the spider shaft 618 when theactuator 656 moves the spider shaft clutch collar 654 in an axialdirection.

A second universal joint 666 is connected to a second pinion shaft 668.A second pinion gear 670 is connected to the second pinion shaft 668.The second pinion shaft 668, and thus the second pinion gear 670, ismounted for rotation within a second wheel differential housing 671. Thesecond pinion gear 670 may be such as a spiral bevel, or it may be ahypoid.

The second pinion shaft 668 is connected to a yoke (not shown) at afirst end portion 672. The yoke is connected to the propeller shaft 653,such as through the second universal joint 666.

The second pinion shaft 668 also has a middle portion 674 and a secondend portion 676. The middle portion 674 may be supported by one or morebearings 614 to facilitate the rotation of the second pinion shaft 668within the second wheel differential housing 671. The second pinion gear670 is drivingly engaged with a second axle driving gear 677. The secondpinion gear 670 may be engaged with the second axle driving gear 677 ina hypoid type arrangement, but other embodiments are permissible aswell. The second pinion shaft 668 is drivingly engaged with the secondaxle driving gear 677 of the second axle assembly 604 through a singlegear mesh.

The second axle driving gear 677 is mounted on, or connected, to asecond wheel differential case 678. At least two pinion gears 680 and atleast two side gears 682 are located within the second wheeldifferential case 678. As known by those skilled in the art, the piniongears 680 and the side gears 682 are connected to one another. The sidegears 682 are also connected to axle half shafts 684.

The second axle driving gear 677 may have the same or a greater diameterthan the first axle driving gear 631. By way of example only, the firstaxle driving gear 631 may have a diameter of approximately 14 inches,while the second axle driving gear 677 may have a diameter ofapproximately 18 inches.

The drive axle system 600 may be placed in a first mode of operation anda second mode of operation. In the first mode of operation, the firstaxle assembly 602 is disengaged and the second axle assembly 604 isengaged. In the second mode of operation, the first axle assembly 602and the second axle assembly 604 is engaged and driven through theinter-axle differential 621.

To place the drive axle system 600 in the first mode of operation, theoutput shaft clutch collar 645 is placed in driving engagement with thefirst axle input shaft 606 and the output shaft 647. Further, thelocking collar 642 of the shaft clutch 636 is placed in the firstposition and the spider shaft clutch collar 654 is placed solely inengagement with the first engagement portion 613. When the spider shaftclutch collar 654 is placed solely in engagement with the firstengagement portion 613, the spider shaft 618 is non-driven, causing thepinion gears 622 and the second axle side gear 624 to be placed in anon-driven state as well. Because the locking collar 642 of the shaftclutch 636 is placed in the first position, the first axle driving gear631, the first pinion shaft 626, the second drop gear 625, and the firstdrop gear 623 are drivingly disengaged from the axle half shafts 635,allowing the first axle driving gear 631, the first pinion shaft 626,the second drop gear 625, and the first drop gear 623 to remain in anon-moving state when the drive axle system 600 is placed in the firstmode of operation. The drive axle system 600 placed in the first mode ofoperation is employed where a single axle drive and a high speed and lowtorque manner of operation is desired.

To place the drive axle system 600 in the second mode of operation, theoutput shaft clutch collar 645 is placed in driving engagement with theside gear teeth formed on the second axle side gear 624 and the outputshaft 647. Further, the locking collar 642 of the shaft clutch 636 isplaced in the second position and the spider shaft clutch collar 654 isplaced in engagement with the first engagement portion 613 and thespider engagement end 620 of the spider shaft 618. When the output shaftclutch collar 645 is placed in driving engagement with the second axleside gear 624 and the output shaft 647, and the spider shaft clutchcollar 654 is placed in engagement with the first engagement portion 613and the spider engagement end 620 of the spider shaft 618, the piniongears 622 on the pinion end 619 drivingly engage the second axle sidegear 624 and the first drop gear 623. Because the locking collar 642 ofthe shaft clutch 636 is placed in the second position, the first axledriving gear 631 drivingly engages the axle half shafts 635 and thus thewheel ends 637. The drive axle system 600 placed in the second mode ofoperation is employed where a multi-axle drive and a low speed and hightorque manner of operation is desired.

The first axle assembly 602 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thefirst axle assembly 602 using the output shaft clutch collar 645 and thespider shaft clutch collar 654, an efficiency over a full time drivenfirst and second axle assembly 602, 604 is achieved by minimizing axlewindage and parasitic drag losses.

The first axle assembly 602 may be selectively and automatically engagedby an automated system that comprises wheel speed sensors and a controlalgorithm that eliminates the need for driver control. In such asituation, the first axle assembly 602 can be automatically engaged atvehicle start up or when the vehicle is in a substantially non-movingstate to proportion the drive torque between the first and second axleassemblies 602, 604. This has the effect of lowering the maximum torqueon either the first and second axle assemblies 602, 604.

FIG. 7 depicts yet another embodiment of the present invention. Theembodiment shown in FIG. 7 is similar to the embodiment shown in FIG. 6.Similar features of the embodiment shown in FIG. 7 are numberedsimilarly in series, with the exception of the features described below.

A second axle side gear 786, in addition to a plurality of side gearteeth formed thereon, includes a conical engagement surface 788 and aset of clutch teeth formed thereon. One or more bearings (not shown) andtheir associated races may be located about the second axle side gear786 to facilitate rotation of the second axle side gear 786 within afirst axle assembly housing 716.

An output shaft synchronizer 790 is located radially outward from andconcentric with at least a portion of a first axle input shaft 706. Theoutput shaft synchronizer 790 may be connected to an actuator 792, suchas a shift fork, for selectively moving the output shaft synchronizer790 in an axial direction. The output shaft synchronizer 790 may have acircumferential groove located in an outer surface thereof. The shiftfork may engage with all or a portion of the circumferential groove tomove the output shaft synchronizer 790 in the axial direction.

The output shaft synchronizer 790 has an inner surface with a first setof teeth and a second set of teeth formed thereon. The first set ofteeth may be located on a front portion of the inner surface of theoutput shaft synchronizer 790 while the second set of teeth are locatedon an rear side of the inner surface of the output shaft synchronizer790.

The first set of teeth formed on the inner surface of the output shaftsynchronizer 790 may selectively engage with either the set of teethformed on a second end portion 712 of the first axle input shaft 706 orthe set of clutch teeth formed on the second axle side gear 786. Thesecond set of teeth formed on the inner surface of the output shaftsynchronizer 790 is always engaged with a set of teeth on an outersurface of an output shaft 747. The set of teeth on the outer surface ofthe output shaft 747 have a predetermined axial length. The length ofteeth formed on the output shaft 747 is sufficient to permit the secondset of teeth formed on the output shaft synchronizer 790 to always beengaged therewith regardless of the axial position of the output shaftsynchronizer 790.

A synchronizer ring 794 is an annular body coupled to the output shaftsynchronizer 790 adjacent the second end portion 712 of the first axleinput shaft 706. The synchronizer ring 794 is shaped to correspond tothe conical engagement surface 788. Alternately, the synchronizer ring794 may have an engagement surface having any other shape. A biasingmember (not shown) is disposed between the output shaft synchronizer 790and the synchronizer ring 794 to urge the synchronizer ring 794 awayfrom the output shaft synchronizer 790. When the output shaftsynchronizer 790 is moved to engage the first set of teeth formed on theinner surface of the output shaft synchronizer 790 with the set ofclutch teeth formed on the second axle side gear 786, the synchronizerring 794 contacts the conical engagement surface 788 of the second axleside gear 786 in variable engagement prior to engaging the first set ofteeth formed on the inner surface of the output shaft synchronizer 790with the set of clutch teeth formed on the second axle side gear 786.

The drive axle system 700 may be placed in a first mode of operation anda second mode of operation. In the first mode of operation, the firstaxle assembly 702 is disengaged and the second axle assembly 704 isengaged. In the second mode of operation, the first axle assembly 702and the second axle assembly 704 is engaged and driven through theinter-axle differential 721.

To place the drive axle system 700 in the first mode of operation, theoutput shaft synchronizer 790 is placed in driving engagement with thefirst axle input shaft 706 and the output shaft 747. Further, thelocking collar 742 of the shaft clutch 736 is placed in the firstposition and the spider shaft clutch collar 754 is placed solely inengagement with the first engagement portion 713. When the spider shaftclutch collar 754 is placed solely in engagement with the firstengagement portion 713, the spider shaft 718 is non-driven, causing thepinion gears 722 and the second axle side gear 786 to be placed in anon-driven state as well. Because the locking collar 742 of the shaftclutch 736 is placed in the first position, the first axle driving gear731, the first pinion shaft 726, the second drop gear 725, and the firstdrop gear 723 are drivingly disengaged from the axle half shafts 735,allowing the first axle driving gear 731, the first pinion shaft 726,the second drop gear 725, and the first drop gear 723 to remain in anon-moving state when the drive axle system 700 is placed in the firstmode of operation. The drive axle system 700 placed in the first mode ofoperation is employed where a single axle drive and a high speed and lowtorque manner of operation is desired.

The output shaft synchronizer 790 facilitates placing the drive axlesystem 700 in the second mode of operation without stopping a vehiclethe drive axle system 700 is incorporated in. To place the drive axlesystem 700 in the second mode of operation, the output shaftsynchronizer 790 is placed in driving engagement with the side gearteeth formed on the second axle side gear 786 and the output shaft 747.Further, the locking collar 742 of the shaft clutch 736 is placed in thesecond position and the spider shaft clutch collar 754 is placed inengagement with the first engagement portion 713 and the spiderengagement end 720 of the spider shaft 718. When the output shaftsynchronizer 790 is placed in driving engagement with the second axleside gear 786 and the output shaft 747, and the spider shaft clutchcollar 754 is placed in engagement with the first engagement portion 713and the spider engagement end 720 of the spider shaft 718, the piniongears 722 on the pinion end 719 drivingly engage the second axle sidegear 786 and the first drop gear 723. Because the locking collar 742 ofthe shaft clutch 736 is placed in the second position, the first axledriving gear 731 drivingly engages the axle half shafts 735 and thus thewheel ends 737. The drive axle system 700 placed in the second mode ofoperation is employed where a multi-axle drive and a low speed and hightorque manner of operation is desired.

The first axle assembly 702 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thefirst axle assembly 702 using the output shaft synchronizer 790 and thespider shaft clutch collar 754, an efficiency over a full time drivenfirst and second axle assembly 702, 704 is achieved by minimizing axlewindage and parasitic drag losses.

The first axle assembly 702 may be selectively and automatically engagedby an automated system that comprises wheel speed sensors and a controlalgorithm that eliminates the need for driver control. In such asituation, the first axle assembly 702 can be automatically engaged atvehicle start up or when the vehicle is in a substantially non-movingstate to proportion the drive torque between the first and second axleassemblies 702, 704. This has the effect of lowering the maximum torqueon either the first and second axle assemblies 702, 704.

FIG. 8 depicts yet another embodiment of the present invention. Theembodiment shown in FIG. 8 is similar to the embodiment shown in FIG. 6.Similar features of the embodiment shown in FIG. 8 are numberedsimilarly in series, with the exception of the features described below.

A spider shaft 857 is rotatably disposed about the first axle inputshaft 806. One or more bearings (not shown) and their associated racesmay be located about the first axle input shaft 806 or the spider shaft857 to facilitate rotation of the first axle input shaft 806 within thefirst axle assembly housing 816. The spider shaft 857 includes a pinionend 858 and a spider engagement end 859.

The pinion end 858 extends radially outward circumferentially from thefirst axle input shaft 806. The pinion end is part of an inter-axledifferential 821 which also comprises a plurality of pinion gears 822.Each of the pinion gears 822 may be a bevel type pinion gear. At leasttwo pinion gears 822 are located on the pinion end 858, and more may beused. The pinion end 858 may extend through an aperture formed in eachof the pinion gears 822.

The spider engagement end 859 extends radially outward circumferentiallyfrom the first axle input shaft 806 opposite the pinion end 858 of thespider shaft 857. The spider engagement end 859 is positioned adjacentthe first engagement portion 813 of the first axle input shaft 806. Thespider engagement end 859 includes a conical engagement surface 860 anda set of clutch teeth formed thereon.

A spider shaft synchronizer 862 is located radially outward from andconcentric with at least a portion of a first axle input shaft 806. Thespider shaft synchronizer 862 may be connected to an actuator 864, suchas a shift fork, for selectively moving the spider shaft synchronizer862 in an axial direction. The spider shaft synchronizer 862 may have acircumferential groove located in an outer surface thereof. The shiftfork may engage with all or a portion of the circumferential groove tomove the spider shaft synchronizer 862 in the axial direction.

The spider shaft synchronizer 862 has an inner surface with a set ofteeth formed thereon. The set of teeth formed on the inner surface ofthe spider shaft synchronizer 862 may selectively engage with the set ofclutch teeth formed on the spider engagement end 859. The set of teethformed on the inner surface of the spider shaft synchronizer 862 isalways engaged with the set of clutch teeth formed on the first axleinput shaft 806 adjacent the first end portion 813. The set of teethformed on the first axle input shaft 806 have a predetermined axiallength. The length of teeth formed on the first axle input shaft 806 issufficient to permit the set of teeth formed on the inner surface of thespider shaft synchronizer 862 to always be engaged therewith regardlessof the axial position of the spider shaft synchronizer 862.

A synchronizer ring 865 is an annular body coupled to the spider shaftsynchronizer 862 adjacent the spider engagement end 859 of the spidershaft 857. The synchronizer ring 865 is shaped to correspond to theconical engagement surface 860. Alternately, the synchronizer ring 865may have an engagement surface having any other shape. A biasing member(not shown) is disposed between the spider shaft synchronizer 862 andthe synchronizer ring 865 to urge the synchronizer ring 865 away fromthe spider shaft synchronizer 862. When the spider shaft synchronizer862 is moved to engage the first set of teeth formed on the innersurface of the spider shaft synchronizer 862 with the set of clutchteeth formed on the spider engagement end 859, the synchronizer ring 865contacts the conical engagement surface 860 of the spider shaft 857 invariable engagement prior to engaging the first set of teeth formed onthe inner surface of the spider shaft synchronizer 862 with the set ofclutch teeth formed on the spider engagement end 859.

A second axle side gear 886, in addition to a plurality of side gearteeth formed thereon, includes of a conical engagement surface 888 and aset of clutch teeth formed thereon. One or more bearings (not shown) andtheir associated races may be located about the second axle side gear886 to facilitate rotation of the second axle side gear 886 within afirst axle assembly housing 816.

An output shaft synchronizer 890 is located radially outward from andconcentric with at least a portion of a first axle input shaft 806. Theoutput shaft synchronizer 890 may be connected to an actuator 892, suchas a shift fork, for selectively moving the output shaft synchronizer890 in an axial direction. The output shaft synchronizer 890 may have acircumferential groove located in an outer surface thereof. The shiftfork may engage with all or a portion of the circumferential groove tomove the output shaft synchronizer 890 in the axial direction.

The output shaft synchronizer 890 has an inner surface with a first setof teeth and a second set of teeth formed thereon. The first set ofteeth may be located on a front portion of the inner surface of theoutput shaft synchronizer 890 while the second set of teeth are locatedon an rear side of the inner surface of the output shaft synchronizer890.

The first set of teeth formed on the inner surface of the output shaftsynchronizer 890 may selectively engage with either the set of teethformed on a second end portion 812 of the first axle input shaft 806 orthe set of clutch teeth formed on the second axle side gear 886. Thesecond set of teeth formed on the inner surface of the output shaftsynchronizer 890 is always engaged with a set of teeth on an outersurface of an output shaft 847. The set of teeth on the outer surface ofthe output shaft 847 have a predetermined axial length. The length ofteeth formed on the output shaft 847 is sufficient to permit the secondset of teeth formed on the output shaft synchronizer 890 to always beengaged therewith regardless of the axial position of the output shaftsynchronizer 890.

A synchronizer ring 894 is an annular body coupled to the output shaftsynchronizer 890 adjacent the second end portion 812 of the first axleinput shaft 806. The synchronizer ring 894 is shaped to correspond tothe conical engagement surface 888. Alternately, the synchronizer ring894 may have an engagement surface having any other shape. A biasingmember (not shown) is disposed between the output shaft synchronizer 890and the synchronizer ring 894 to urge the synchronizer ring 894 awayfrom the output shaft synchronizer 890. When the output shaftsynchronizer 890 is moved to engage the first set of teeth formed on theinner surface of the output shaft synchronizer 890 with the set ofclutch teeth formed on the second axle side gear 886, the synchronizerring 894 contacts the conical engagement surface 888 of the second axleside gear 886 in variable engagement prior to engaging the first set ofteeth formed on the inner surface of the output shaft synchronizer 890with the set of clutch teeth formed on the second axle side gear 886.

The drive axle system 800 may be placed in a first mode of operation anda second mode of operation. In the first mode of operation, the firstaxle assembly 802 is disengaged and the second axle assembly 804 isengaged. In the second mode of operation, the first axle assembly 802and the second axle assembly 804 is engaged and driven through theinter-axle differential 821.

To place the drive axle system 800 in the first mode of operation, theoutput shaft synchronizer 890 is placed in driving engagement with thefirst axle input shaft 806 and the output shaft 847 and the spider shaftsynchronizer 862 is placed solely in driving engagement with the set ofclutch teeth formed on the spider engagement end 859. Further, thelocking collar 842 of the shaft clutch 836 is placed in the firstposition. When the spider shaft synchronizer 862 is placed solely inengagement with the spider engagement end 859, the spider shaft 857 isnon-driven, causing the pinion gears 822 and the second axle side gear886 to be placed in a non-driven state as well. Because the lockingcollar 842 of the shaft clutch 836 is placed in the first position, thefirst axle driving gear 831, the first pinion shaft 826, the second dropgear 825, and the first drop gear 823 are drivingly disengaged from theaxle half shafts 835, allowing the first axle driving gear 831, thefirst pinion shaft 826, the second drop gear 825, and the first dropgear 823 to remain in a non-moving state when the drive axle system 800is placed in the first mode of operation. The drive axle system 800placed in the first mode of operation is employed where a single axledrive and a high speed and low torque manner of operation is desired.

The output shaft synchronizer 890 and the spider shaft synchronizer 862facilitate placing the drive axle system 800 in the second mode ofoperation without stopping a vehicle the drive axle system 800 isincorporated in. Prior to placing the drive axle system 800 in thesecond mode of operation, the spider shaft synchronizer 862 or theoutput shaft synchronizer 890 may be variably engaged to “spool up” thefirst axle driving gear 831, the first pinion shaft 826, the second dropgear 825, and the first drop gear 823 to permit the shaft clutch 836 tobe engaged without stopping the vehicle the drive axle system 800 isincorporated in.

To place the drive axle system 800 in the second mode of operation, theoutput shaft synchronizer 890 is placed in driving engagement with theside gear teeth formed on the second axle side gear 886 and the outputshaft 847 and the spider shaft synchronizer 862 is placed in engagementwith the first engagement portion 813 and the spider engagement end 859of the spider shaft 857. Further, the locking collar 842 of the shaftclutch 836 is placed in the second position. When the output shaftsynchronizer 890 is placed in driving engagement with the second axleside gear 886 and the output shaft 847, and the spider shaftsynchronizer 862 is placed in engagement with the first engagementportion 813 and the spider engagement end 859 of the spider shaft 857,the pinion gears 822 on the pinion end 858 drivingly engage the secondaxle side gear 886 and the first drop gear 823. Because the lockingcollar 842 of the shaft clutch 836 is placed in the second position, thefirst axle driving gear 831 drivingly engages the axle half shafts 835and thus the wheel ends 837. The drive axle system 800 placed in thesecond mode of operation is employed where a multi-axle drive and a lowspeed and high torque manner of operation is desired.

The first axle assembly 802 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thefirst axle assembly 802 using the output shaft synchronizer 890 and thespider shaft synchronizer 862, an efficiency over a full time drivenfirst and second axle assembly 802, 804 is achieved by minimizing axlewindage and parasitic drag losses.

The first axle assembly 802 may be selectively and automatically engagedby an automated system that comprises wheel speed sensors and a controlalgorithm that eliminates the need for driver control. In such asituation, the first axle assembly 802 can be automatically engaged atvehicle start up to proportion the drive torque between the first andsecond axle assemblies 802, 804. This has the effect of lowering themaximum torque on either the first and second axle assemblies 802, 804.

FIG. 9 depicts yet another embodiment of the present invention. FIG. 9depicts a drive axle system 900 comprised of a first axle assembly 902and a second axle assembly 904.

The first axle assembly 902 includes a first axle input shaft 906 with afirst end portion 908, a middle portion 910 and a second end portion912. The first end portion 908 is connected to a source of rotationalpower, such as a transmission or an engine. A first engagement portion913 including a first set of clutch teeth extends radially from thefirst axle input shaft 906 adjacent the first end portion 908.Preferably, the first set of clutch teeth is unitary with the first axleinput shaft. However, it is permissible for them to be located on acollar that is splined to the input shaft 906. One or more bearings 914and their associated races may be located about the first end portion908 to facilitate rotation of the first axle input shaft 906 within afirst axle assembly housing 916.

A second set of teeth are also provided on the second end portion 912 ofthe first axle input shaft 906. It is also preferred that these teethare unitary with the first axle input shaft 906, but they may also belocated on a splined collar. The middle portion 910 between the firstset of teeth and the second set of teeth may have a substantiallyconstant diameter.

A carrier 917 is located radially outward from and concentric with themiddle portion 910 of the first axle input shaft 906. The carrier 917comprises a first end portion, a middle portion and a second endportion. Preferably, all of the portions are unitary with one another.

The first end portion of the carrier 917 is adjacent the first set ofteeth on the first axle input shaft 906. The first end portion of thecarrier 917 also has a set of clutch teeth 918 located thereon.Preferably, the clutch teeth 918 are unitary with the first end portionof the carrier 917 and extend primarily radially outward.

The middle portion of the carrier 917 is substantially constant in itsdiameter and may extend along a portion of the first axle input shaft906. The second end portion of the carrier 917 is comprised of aradially extending portion and at least one planet gear pinion mount919. The at least one planet gear pinion mount 919 extends transverselyto the radially extending portion of the carrier 917 in the outboarddirection so as to be parallel to the middle portion of the carrier 917as well as middle portion of the first axle input shaft 906. A pluralityof planet gear pinions 920 are rotatably mounted on each of the planetgear pinion mounts 919. A gap exists between the middle portion of thecarrier 917 and each of the planet gear pinions 920.

A sun gear 921 is located radially outward and concentric with themiddle portion of the carrier 917. The sun gear 921 has a set ofoutboard teeth and a set of inboard teeth. The set of outboard teeth andthe set of inboard teeth are primarily oriented radially outward. Asshown in FIG. 9, the set of outboard teeth are located adjacent thefirst end portion of the carrier 917.

The set of inboard teeth of the sun gear 921 are located adjacent thegap between the middle portion of the carrier 917 and each of the planetgear pinions 920. More particularly, the set of inboard teeth of the sungear 921 are located radially inward from the planet gear pinions 920and are in driving engagement with the planet gear pinions 920.

The planet gear pinions 920 are engaged with an outer ring 922. Moreparticularly, the planet gear pinions 920 are engaged with a set ofinner teeth 923 located in an inner surface of the outer ring 922.

The outer ring 922 extends axially over the radially extending portionof the carrier 917 to a set of outer teeth 924 located on an outersurface of the outer ring 922. The set of outer teeth 924 on the outerring 922 is located adjacent the second end portion 912 of the firstaxle input shaft 906.

The set of outboard teeth of the sun gear 921 are meshed with a set ofteeth of a drop gear 925. The drop gear 925 is concentric with a firstpinion shaft 926 located below the first axle input shaft 906. Thesecond drop gear 925 may have a splined inner surface that engages witha splined outer surface of the first pinion shaft 926. The second dropgear 925 is located on a first end portion 927 of the first pinion shaft926.

The first pinion shaft 926 also has a middle portion 928 and a secondend portion 929. The middle portion 928 may be supported for rotationwithin the first axle assembly housing 916 by one or more bearings 914and their associated races. The second end portion 929 includes a firstpinion gear 930 disposed thereon.

The first pinion gear 930 is located in driving engagement with a firstaxle driving gear 931, such as in a hypoid orientation. Otherorientations of the first axle driving gear 931 and the first piniongear 930 are also permissible.

The first axle driving gear 931 is mounted on, or connected, to a firstwheel differential case 932. At least two pinion gears 933 and at leasttwo side gears 934 are located within the first wheel differential case932. As known by those skilled in the art, the pinion gears 933 and theside gears 934 are connected to one another. The side gears 934 are alsoconnected to axle half shafts 935.

A shaft clutch 936 is mounted to one of the axle half shafts 935 anddivides the axle half shaft 935 into a first portion 938 and a secondportion 939. The shaft clutch 936 may be a splined dog type clutch. Theshaft clutch 936 comprises a first toothed portion 940 formed on thefirst portion 938 and a second toothed portion 941 formed on the secondportion 939. The first toothed portion 940 and the second toothedportion 941 may be directed formed on the first portion 938 and thesecond portion 939 or they may be formed on a sleeve located about thefirst portion 938 and the second portion 939. The first toothed portion940 and the second toothed portion 941 respectively rotate with thefirst portion 938 and the second portion 939 of one of the axle halfshafts 935.

The shaft clutch 936 further comprises a locking collar 942 disposedabout one of the axle half shafts 935 and drivingly engaged with atleast one of the first toothed portion 940 and the second toothedportion 941. The locking collar 942 is axially moveable along the firsttoothed portion 940 and the second toothed portion 941 and includes aplurality of teeth formed on an inner surface thereof. The lockingcollar 942 has a first position and a second position. As shown in FIG.9, the locking collar 942 is in the first position and is drivinglyengaged with the first toothed portion 940. In the second position, thelocking collar 942 is drivingly engaged with the first toothed portion940 and the second toothed portion 941, causing the first portion 938 tobe drivingly engaged with the second portion 939.

The locking collar 942 may be selectively moved along the first toothedportion 940 and the second toothed portion 941 so as to couple the firstportion 938 and the second portion 939. The locking collar 942 may bemoved by an actuator 943 such as a pneumatic actuator, anelectromechanical actuator, or a hydraulic actuator. The actuator 943may be connected to the anti-lock braking system of the vehicle, asdescribed below.

The axle half shafts 935 are connected to wheel ends 944. Each wheel end944 supports wheels and tires (not shown).

The shaft clutch 936 permits the second portion 939 to be selectivelydisengaged from the side gear 934, the first axle driving gear 931, thefirst pinion shaft 926, the second drop gear 925, and thus the firstdrop gear 923. As a result, the first axle driving gear 931 and thefirst pinion shaft 926 can idle during vehicle operation.

The first axle input shaft 906 is provided with the second set of teethformed on the second end portion 912 for engaging an output shaft clutchcollar 945. The second set of teeth formed on the second end portion 912are located axially adjacent the outer teeth 924 formed on the outerring 922.

The output shaft clutch collar 945 is located radially outward from andconcentric with at least a portion of the first axle input shaft 906.The output shaft clutch collar 945 may be connected to an actuator 946,such as a shift fork, for selectively moving the output shaft clutchcollar 945 in an axial direction. The output shaft clutch collar 945 mayhave a circumferential groove located in an outer surface thereof. Theshift fork may engage with all or a portion of the circumferentialgroove to move the output shaft clutch collar 945 in the axialdirection.

The output shaft clutch collar 945 has an inner surface with a first setof teeth and a second set of teeth formed thereon. The first set ofteeth may be located on a front portion of the inner surface of theoutput shaft clutch collar 945 while the second set of teeth are locatedon an rear side of the inner surface of the output shaft clutch collar945.

The first set of teeth formed on the inner surface of the output shaftclutch collar 945 may selectively engage with either the set of teethformed on the second end portion 912 of the first axle input shaft 906or the outer teeth 924 formed on the outer ring 922. The second set ofteeth formed on the inner surface of the output shaft clutch collar 945is always engaged with a set of teeth on an outer surface of an outputshaft 947. The set of teeth on the outer surface of the output shaft 947have a predetermined axial length. The length of teeth formed on theoutput shaft 947 is sufficient to permit the second set of teeth formedon the output shaft clutch collar 945 to always be engaged therewithregardless of the axial position of the output shaft clutch collar 945.

The output shaft 947 comprises a first end portion 948, a middle portion949, and a second end portion 950. The set of teeth on the outer surfaceof the output shaft 947 are formed on the first end portion 948. Thefirst end portion 948 may also define an inner axial cavity 951 designedto receive at least a portion of the second end portion 912 of the firstaxle input shaft 906 therein.

The middle portion 949 of the output shaft 947 may be supported by oneor more bearings 914 and their associated races. The bearings 914facilitate rotation of the output shaft 947 within the first axleassembly housing 916.

The second end portion 950 comprises a yoke (not shown) for connectingwith a first universal joint 952. The first universal joint 952 isconnected to a propeller shaft 953. The propeller shaft 953 extendsbetween the first axle assembly 902 and the second axle assembly 904.

The set of clutch teeth formed on the first engagement portion 913 ofthe first axle input shaft 906 engage a carrier clutch collar 954.Preferably, set of clutch teeth formed on the first engagement portion913 are unitary with the first axle input shaft 906. However, it ispermissible for the teeth to be located on a collar that is splined tothe first axle input shaft 906. The set of clutch teeth formed on thefirst engagement portion 913 are located axially adjacent the set ofclutch teeth 918 formed on the first end portion of the carrier 917.

The carrier clutch collar 954 is located radially outward from andconcentric with at least a portion of the first axle input shaft 906.The carrier clutch collar 954 may be connected to the actuator 956, suchas a shift fork, for selectively moving the carrier clutch collar 954 inan axial direction. The carrier clutch collar 954 may have acircumferential groove located in an outer surface thereof. The shiftfork may engage with all or a portion of the circumferential groove tomove the carrier clutch collar 954 in the axial direction.

The carrier clutch collar 954 has an inner surface with a set of teethformed thereon. The set of teeth formed on the inner surface of thecarrier clutch collar 954 is always engaged with the set of clutch teethformed on the first engagement portion 913. The set of clutch teethformed on the first engagement portion 913 have a predetermined axiallength. The length of the set of clutch teeth formed on the firstengagement portion 913 is sufficient to permit the set of teeth formedon the carrier clutch collar 954 to always be engaged therewithregardless of the axial position of the carrier clutch collar 954. Theset of teeth formed on the inner surface of the carrier clutch collar954 may selectively engage the set of clutch teeth 918 formed on thefirst end portion of the carrier 917 when the actuator 956 moves thecarrier clutch collar 954 in an axial direction.

A second universal joint 966 is connected to a second pinion shaft 968.A second pinion gear 970 is connected to the second pinion shaft 968.The second pinion shaft 968, and thus the second pinion gear 970, ismounted for rotation within a second wheel differential housing 971. Thesecond pinion gear 970 may be such as a spiral bevel, or it may be ahypoid.

The second pinion shaft 968 is connected to a yoke (not shown) at afirst end portion 972. The yoke is connected to the propeller shaft 953,such as through the second universal joint 966.

The second pinion shaft 968 also has a middle portion 974 and a secondend portion 976. The middle portion 974 may be supported by one or morebearings 914 to facilitate the rotation of the second pinion shaft 968within the second wheel differential housing 971. The second pinion gear970 is drivingly engaged with a second axle driving gear 977. The secondpinion gear 970 may be engaged with the second axle driving gear 977 ina hypoid type arrangement, but other embodiments are permissible aswell. The second pinion shaft 968 is drivingly engaged with the secondaxle driving gear 977 of the second axle assembly 904 through a singlegear mesh.

The second axle driving gear 977 is mounted on, or connected, to asecond wheel differential case 978. At least two pinion gears 980 and atleast two side gears 982 are located within the second wheeldifferential case 978. As known by those skilled in the art, the piniongears 980 and the side gears 982 are connected to one another. The sidegears 982 are also connected to axle half shafts 984.

The second axle driving gear 977 may have the same or a greater diameterthan the first axle driving gear 931. By way of example only, the firstaxle driving gear 931 may have a diameter of approximately 14 inches,while the second axle driving gear 977 may have a diameter ofapproximately 18 inches.

The drive axle system 900 may be placed in a first mode of operation anda second mode of operation. In the first mode of operation, the firstaxle assembly 902 is disengaged and the second axle assembly 904 isengaged. In the second mode of operation, the first axle assembly 902and the second axle assembly 904 is engaged and driven through aplanetary inter-axle differential 988 comprised of the carrier 917, theplanet gear pinions 920, and the outer ring 922. It is understood thatwhen the drive axle system 900 is placed in the second mode ofoperation, the planetary inter-axle differential 988 may be configuredto divide torque in an unequal manner between the first axle drivinggear 931 and the second axle driving gear 977 in a predetermined manner.Further, it is understood that the first axle assembly 902 and thesecond axle assembly 904 may be configured with different axle ratios.When the first axle assembly 902 and the second axle assembly areconfigured with different axle ratios, the planetary inter-axledifferential 988 permits the different axle ratios to be blended whenthe drive axle system 900 is placed in the second mode of operation.

To place the drive axle system 900 in the first mode of operation, theoutput shaft clutch collar 945 is placed in driving engagement with thefirst axle input shaft 906 and the output shaft 947. Further, thelocking collar 942 of the shaft clutch 936 is placed in the firstposition and the carrier clutch collar 954 is placed solely inengagement with the first engagement portion 913. When the carrierclutch collar 954 is placed solely in engagement with the firstengagement portion 913, the carrier 917 is non-driven, causing theplanet gear pinions 620, the sun gear 920, and the outer ring 922 to beplaced in a non-driven state as well. Because the locking collar 942 ofthe shaft clutch 936 is placed in the first position, the first axledriving gear 931, the first pinion shaft 926, and the drop gear 925 aredrivingly disengaged from the axle half shafts 935, allowing the firstaxle driving gear 931, the first pinion shaft 926, and the drop gear 925to remain in a non-moving state when the drive axle system 900 is placedin the first mode of operation. The drive axle system 900 placed in thefirst mode of operation is employed where a single axle drive and a highspeed and low torque manner of operation is desired.

To place the drive axle system 900 in the second mode of operation, theoutput shaft clutch collar 945 is placed in driving engagement with theouter teeth 924 formed on the outer ring 922 and the output shaft 947.Further, the locking collar 942 of the shaft clutch 936 is placed in thesecond position and the carrier clutch collar 954 is placed inengagement with the first engagement portion 913 and the clutch teeth918 of the carrier 917. When the output shaft clutch collar 945 isplaced in driving engagement with the outer teeth 924 formed on theouter ring 922 and the output shaft 947, and the carrier clutch collar954 is placed in engagement with the first engagement portion 913 andthe clutch teeth 918 of the carrier 917, the planet gear pinions 920 onthe planet gear pinion mounts 919 drivingly engage the inner teeth 923of the outer ring 922 and the set of inboard teeth of the sun gear 921.Because the locking collar 942 of the shaft clutch 936 is placed in thesecond position, the first axle driving gear 931 drivingly engages theaxle half shafts 935 and thus the wheel ends 937. The drive axle system900 placed in the second mode of operation is employed where amulti-axle drive and a low speed and high torque manner of operation isdesired.

The first axle assembly 902 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thefirst axle assembly 902 using the output shaft clutch collar 945 and thecarrier clutch collar 954, an efficiency over a full time driven firstand second axle assembly 902, 904 is achieved by minimizing axle windageand parasitic drag losses.

The first axle assembly 902 may be selectively and automatically engagedby an automated system that comprises wheel speed sensors and a controlalgorithm that eliminates the need for driver control. In such asituation, the first axle assembly 902 can be automatically engaged atvehicle start up or when the vehicle is in a substantially non-movingstate to proportion the drive torque between the first and second axleassemblies 902, 904. This has the effect of lowering the maximum torqueon either the first and second axle assemblies 902, 904.

FIG. 10 illustrates a drive axle system 1000 for a vehicle incorporatingan inter-axle differential assembly 1002. The drive axle system 1000preferably includes the inter-axle differential assembly 1002, a firstaxle assembly 1004, and a second axle assembly 1006. As shown, the driveaxle system 1000 includes the three assemblies 1002, 1004, and 1006, butit is understood the drive axle system 1000 may include fewer or moreassemblies or components.

The inter-axle differential assembly 1002 includes an input shaft 1008,a plurality of driving pinions 1010, a transfer shaft 1012, a secondoutput gear 1014, a first output gear 1016, and a shift collar 1018.Preferably, the components 1008, 1010, 1012, 1014, 1016, 1018 are formedfrom a hardened steel, however the components 1008, 1010, 1012, 1014,1016, 1018 may be formed from any other rigid material. As shown, thedrive axle system 1000 includes the six components 1008, 1010, 1012,1014, 1016, 1018 disposed in a housing 1020 but it is understood theinter-axle differential assembly 1002 may include fewer or morecomponents

The input shaft 1008 is at least partially disposed in the housing 1020.Preferably, the input shaft 1008 is an elongate cylindrical member,however the input shaft 1008 may be any other shape. Bearings 1022disposed between the input shaft 1008 and the housing 1020 and the inputshaft 1008 and the transfer shaft 1012 permit the input shaft 1008 torotate about an axis of the input shaft 1008. The input shaft 1008 has afirst end portion 1023, having a first set of clutch gear teeth 1024formed thereon, a middle portion 1025, and a second end portion 1026,having a pinion carrier 1028 disposed thereon.

The first end portion 1023 has a diameter greater than a diameter of themiddle portion 1025. The first end portion 1023 is a substantially discshaped body drivingly coupled to the input shaft 1008. Alternately, thefirst end portion 1023 may be integrally formed with the input shaft1008. The first end portion 1023 includes an engagement portion 1029formed therein adjacent an outer peripheral edge thereof. As shown, theengagement portion 1029 is a conical surface oblique to the input shaft1008, however, the engagement portion 1029 may have any other shape. Thefirst set of clutch gear teeth 1024 are formed on the first end portion1023 intermediate the input shaft 1008 and the engagement portion 1029.

The pinion carrier 1028 is a substantially disc shaped body having aplurality of pinion supports protruding therefrom radially outwardlyfrom a peripheral edge of the pinion carrier 1028. Each of the pluralityof pinion supports is formed perpendicular to the axis of the inputshaft 1008. Alternately, the pinion carrier 1028 may comprise aplurality of cylindrical members protruding radially outwardly from theinput shaft 1008 or a disc shaped body having a plurality of pinionshaft apertures formed therein about a peripheral edge thereof.

The plurality of driving pinions 1010 are rotatably coupled to theplurality of pinion supports of the pinion carrier 1028. Each of thedriving pinions 1010 have gear teeth formed on an outer surface thereof.As is known in the art, each of the driving pinions 1010 is known as aspider gear. Preferably, the driving pinions 1010 are directly mountedon the pinion supports, however, bearings may be disposed between eachof the driving pinions 1010 and the pinion supports.

The transfer shaft 1012 is a hollow shaft concentrically disposed aboutthe input shaft 1008. Preferably, the transfer shaft 1012 is a hollowelongate cylindrical member, however the transfer shaft 1012 may be anyother shape. Bearings 1022 disposed between the transfer shaft 1012 andthe housing 1020 and the input shaft 1008 and the transfer shaft 1012permit the transfer shaft 1012 to rotate about an axis of the transfershaft 1012. The axis of the transfer shaft 1012 is concurrent with theaxis of the input shaft 1008. The transfer shaft 1012 has a first endportion 1030, having a first set of clutch gear teeth 1031 formed on anouter surface thereof, and a second end portion 1032, having a set ofside gear teeth 1033 formed in an outer surface thereof.

The first end portion 1030 and the second end portion 1032 aresubstantially disc shaped bodies having an outer diameter greater than adiameter of the transfer shaft 1012. The first end portion 1030 and thesecond end portion 1032 are drivingly coupled to the transfer shaft1012. Alternately, the first end portion 1030 and the second end portion1032 may be integrally formed with the transfer shaft 1012 and may havea diameter substantially equal to the transfer shaft 1012. Similarly,the first set of clutch gear teeth 1031 and the set of side gear teeth1033 may be formed directly in the transfer shaft 1012. As is known inthe art, the second end portion 1032 having the set of side gear teeth1033 is known as a side gear. The set of side gear teeth 1033 arebeveled gear teeth and are engaged with the plurality of driving pinions1010. The first set of clutch gear teeth 1031 are disposed adjacent thefirst set of clutch gear teeth 1024 of the input shaft 1008.

The first output gear 1016 is a gear concentrically journaled about theinput shaft 1008 adjacent the pinion carrier 1028. The first output gear1016 has a set of side gear teeth 1034 formed in an outer surfacethereof. As is known in the art, the first output gear 1016 having theset of side gear teeth 1034 is known as a side gear. The set of sidegear teeth 1034 are beveled gear teeth and are engaged with theplurality of driving pinions 1010.

The first output gear 1016 includes an output shaft 1035 drivinglycoupled thereto. Alternately, the first output gear 1016 may beintegrally formed with the output shaft 1035. The output shaft 1035 iscollinear with the input shaft 1008. Bearings 1022 disposed between theoutput shaft 1035 and the housing 1020 support the first output gear1016 and permit the output shaft 1035 to rotate about an axis of theoutput shaft 1035.

The second output gear 1014 is a gear concentrically disposed about theinput shaft 1008 and the transfer shaft 1012. The second output gear1014 has a central perforation having a diameter greater than a diameterof the transfer shaft 1012. The second output gear 1014 is asubstantially disc shaped body having a first end portion 1036, a secondend portion 1037 defining an outer diameter of the second output gear1014, and an engagement portion 1038. Bearings (not shown) disposedbetween the transfer shaft 1012 and the second output gear 1014 permitthe second output gear 1014 to rotate about an axis of the second outputgear 1014. The axis of the second output gear 1014 is concurrent withthe axis of the input shaft 1008. A first set of clutch gear teeth 1039are formed on the first end portion 1036 adjacent the first set ofclutch gear teeth 1031 of the transfer shaft 1012. A second set of gearteeth 1040 are formed on the second end portion 1037.

The engagement portion 1038 is formed in the second output gear 1014intermediate the first end portion 1036 and the second end portion 1037.As shown, the engagement portion 1038 is a conical surface oblique tothe input shaft 1008; however, the engagement portion 1038 may have anyother shape.

The shift collar 1018 is concentrically disposed about the input shaft1008 and the transfer shaft 1012. The shift collar 1018 includes a setof inner clutch collar teeth 1041 formed on an inner surface thereof, afirst synchronizer ring 1042, and a second synchronizer ring 1043. Theset of inner clutch collar teeth 1041 are engaged with the first set ofclutch gear teeth 1031 of the transfer shaft 1012. The shift collar 1018can be slidably moved along the axis of the input shaft 1008 as directedmanually by an operator of the vehicle or automatically by an electroniccontrol unit (not shown) while maintaining engagement of the innerclutch collar teeth 1041 and the first set of clutch gear teeth 1031. Ashift fork 1044 disposed in an annular recess formed in the shift collar1018 moves the shift collar 1018 along the axis of the input shaft 1008into a first position, a second position, or a neutral position. A shiftmechanism (not shown), which is drivingly engaged with the shift fork1044, is actuated to position the shift fork 1044 as directed manuallyby an operator of the vehicle or automatically by the electronic controlunit. Consequently, the shift fork 1044 positions the shift collar 1018into the first position, the second position, or the neutral position.In the first position, the shift collar 1018 is drivingly engaged withthe first set of clutch gear teeth 1031 of the transfer shaft 1012 andthe first set of clutch gear teeth 1024 of the input shaft 1008. In thesecond position, the shift collar 1018 is drivingly engaged with thefirst set of clutch gear teeth 1031 of the transfer shaft 1012 and thefirst set of clutch gear teeth 1039 of the second output gear 1014. Inthe neutral position, the inner clutch collar teeth 1041 of the shiftcollar 1018 are only drivingly engaged with the first set of clutch gearteeth 1031 of the transfer shaft 1012. It is understood the shift collar1018, the clutch gear teeth 1024, 1031, 1039, 1041, the synchronizerrings 1042, 1043, and the engagement portions 1029, 1038 may besubstituted with any clutching device that permits selective engagementof a driving and a driven part.

The first synchronizer ring 1042 is an annular body coupled to the shiftcollar 1018 adjacent the first end portion 1023 of the input shaft 1008.The first synchronizer ring 1042 has a first conical engagement surface1045. Alternately, the first synchronizer ring 1042 may have anengagement surface having any other shape. A biasing member (not shown)is disposed between the shift collar 1018 and the first synchronizerring 1042 to urge the first synchronizer ring 1042 away from the shiftcollar 1018. When the shift collar 1018 is moved from the secondposition into the first position, the first conical engagement surface1045 contacts the engagement portion 1029 of the first end portion 1023of the input shaft 1008. As the shift collar 1018 moves towards thefirst set of clutch gear teeth 1024 of the input shaft 1008, the biasingmember is compressed while the shift collar 1018 engages the first setof clutch gear teeth 1031 of the transfer shaft 1012 and before theshift collar 1018 engages the first set of clutch gear teeth 1024 of theinput shaft 1008.

The second synchronizer ring 1043 is an annular body coupled to theshift collar 1018 adjacent the first end portion 1036 of the secondoutput gear 1014. The second synchronizer ring 1043 has a second conicalengagement surface 1046. Alternately, the second synchronizer ring 1043may have an engagement surface having any other shape. A biasing member(not shown) is disposed between the shift collar 1018 and the secondsynchronizer ring 1043 to urge the second synchronizer ring 1043 awayfrom the shift collar 1018. When the shift collar 1018 is moved from thefirst position into the second position, the second conical engagementsurface 1046 contacts the engagement portion 1038 of the first endportion 1036 of the second output gear 1014. As the shift collar 1018moves towards the first set of clutch gear teeth 1039 of the secondoutput gear 1014, the biasing member is compressed while the shiftcollar 1018 engages the first set of clutch gear teeth 1031 of thetransfer shaft 1012 and before the shift collar 1018 engages the firstset of clutch gear teeth 1039 of the second output gear 1014.

A bevel gear pinion 1049 is drivingly coupled to the output shaft 1035opposite the first output gear 1016. Alternately, the bevel gear pinion1049 may be integrally formed with the output shaft 1035. As is known inthe art, the bevel gear pinion 1049 has gear teeth formed on an outersurface thereof. The bevel gear pinion 1049 may be one of a hypoid gear,a spiral bevel gear, a straight bevel gear, or any other gear known tothose skilled in the art.

The first axle assembly 1004 includes the bevel gear pinion 1049, afirst driving gear 1050, a first wheel differential 1051, and a firstpair of output axles 1052. Preferably, the components 1049, 1050, 1051,1052 are formed from a hardened steel, however the components 1049,1050, 1051, 1052 may be formed from any other rigid material. As shown,the first axle assembly 1004 includes the four components 1049, 1050,1051, 1052 disposed in a first axle housing 1053 but it is understoodthe first axle assembly 1004 may include fewer or more components.

The first driving gear 1050 is coupled to a housing of the first wheeldifferential 1051 by a plurality of fasteners or a weld and is rotatableabout an axis of the first pair of output axles 1052 within the firstaxle housing 1053. Alternately, the first driving gear 1050 may beintegrally formed with the first wheel differential 1051. As is known inthe art, the first driving gear 1050 has gear teeth formed on an outersurface thereof. The first driving gear 1050 may be one of a hypoidgear, a spiral bevel gear, a straight bevel gear, or any other gearknown to those skilled in the art. The first driving gear 1050 isdrivingly engaged with the bevel gear pinion 1049 and has a first gearratio. As a non-limiting example, the first gear ratio may be a 2.42:1ratio, but it is understood that other ratios may be used. The outputshaft 1035 is drivingly engaged with the first driving gear 1050 of thefirst axle assembly 1004 through a single gear mesh.

The first wheel differential 1051 is a bevel gear style differential asis known in the art having a plurality of driving pinions and a pair ofside gears drivingly engaged with the first pair of output axles 1052.The first wheel differential 1051 is rotatably disposed within the firstaxle housing 1053 about the axis of the first pair of output axles 1052.Alternately, other styles of differentials may be used in place of thefirst wheel differential 1051.

The first pair of output axles 1052 are elongate cylindrical membershaving a common axis rotatably mounted within the first axle housing1053. Bearings 1022 disposed between the first pair of output axles 1052and the first axle housing 1053 permit the first pair of output axles1052 to rotate therein. The side gears of the first wheel differential1051 are disposed on first ends of each of the first output axles 1052and wheels (not shown) are disposed on second ends of each of the firstoutput axles 1052.

The second axle assembly 1006 includes an inter-axle shaft 1054, asecond driving gear 1056, a second wheel differential 1057, a pair ofsecond output axles 1058, and an axle clutch 1059. Preferably, thecomponents 1054, 1056, 1057, 1058, 1059 are formed from a hardenedsteel, however the components 1054, 1056, 1057, 1058, 1059 may be formedfrom any other rigid material. As shown, the second axle assembly 1006includes the five components 1054, 1056, 1057, 1058, 1059 disposed in asecond axle housing 1060 but it is understood the second axle assembly1006 may include fewer or more components.

The inter-axle shaft 1054 comprises at least one elongate cylindricalmember drivingly engaged with the second output gear 1014 through adriven gear 1062 coupled to the inter-axle shaft 1054. As illustrated,the inter-axle shaft 1054 comprises a plurality of elongate cylindricalmembers connected by joints. Bearings 1022 disposed between theinter-axle shaft 1054 and the housing 1020 permit the inter-axle shaft1054 to rotate therein.

A bevel gear pinion 1064 is drivingly coupled to the inter-axle shaft1054 opposite the driven gear 1062. As is known in the art, the bevelgear pinion 1064 has gear teeth formed on an outer surface thereof. Thebevel gear pinion 1064 may be one of a hypoid gear, a spiral bevel gear,a straight bevel gear, or any other gear known to those skilled in theart.

The second driving gear 1056 is a ring style bevel gear as is known inthe art having a set of gear teeth engaged with the gear teeth formed onthe bevel gear pinion 1064. The second driving gear 1056 is coupled to ahousing of the second wheel differential 1057 by a plurality offasteners or a weld and is rotatable about an axis of the pair of secondoutput axles 1058 within the second axle housing 1060. Alternately, thesecond driving gear 1056 may be integrally formed with the second wheeldifferential 1057. The second driving gear 1056 is drivingly engagedwith the bevel gear pinion 1064 and has a second gear ratio.

The second wheel differential 1057 is a bevel gear style differential asis known in the art having a plurality of driving pinions and a pair ofside gears drivingly engaged with the pair of second output axles 1058.The second wheel differential 1057 is rotatably disposed within thesecond axle housing 1060 about the axis of the pair of second outputaxles 1058. Alternately, other styles of differentials may be used inplace of the second wheel differential 1057.

The pair of second output axles 1058 are elongate cylindrical membershaving a common axis rotatably mounted within the second axle housing1060. Bearings 1022 disposed between the pair of second output axles1058 and the second axle housing 1060 permit the first pair of secondoutput axles 1058 to rotate therein. The side gears of the second wheeldifferential 1057 are disposed on first ends of each of the secondoutput axles 1058 and wheels (not shown) are disposed on second ends ofeach of the second output axles 1058.

The axle clutch 1059 is a dog style clutch that divides one of thesecond output axles 1058 into first and second portions. Alternately,the axle clutch 1059 may be a component of the second wheel differential1057 which engages a side gear of the second wheel differential 1057 andone of the second output axles 1058. The axle clutch 1059 may also be aplate style clutch or any other style clutch. A shift collar 1065slidingly disposed on a first component of the axle clutch 1059selectively engages a plurality of teeth formed thereon withcorresponding teeth formed on a first component and a second componentof the axle clutch 1059. The shift collar 1065 is urged into an engagedposition or a disengaged position by a shift fork 1066. When the axleclutch 1059 is in the engaged position, the first portion of one of thesecond output axles 1058 is drivingly engaged with the second portion ofone of the second output axles 1058.

In use, the drive axle system 1000 facilitates a low speed and hightorque multi-axle manner of operation and a high speed and low torquesingle axle manner of operation. The manner of operation of the driveaxle system 1000 is determined by a position of the shift collar 1018.The drive axle system 1000 balances a rotational difference between thefirst output gear 1016 and the second output gear 1014 caused by adifference between the first gear ratio and the second gear ratio withthe inter-axle differential, wherein the balancing of the rotationaldifference between the first output gear 1016 and the second output gear1014 provides a cumulative gear ratio for the first axle assembly 1004and the second axle assembly 1006. The cumulative gear ratio isintermediate the first gear ratio and the second gear ratio.

Upon having recognized the circumstances that the high speed and lowtorque single axle manner of operation of the drive axle system 1000 isadvantageous in, the operator of the vehicle the drive axle system 1000is incorporated in shifts the drive axle system 1000 into the firstposition. As a non-limiting example, circumstances in which the operatormay recognize as being advantageous for the high speed and low torquesingle axle manner of operation are operation of the vehicle notburdened by a load and operation of the vehicle at highway speeds. Whenthe shift collar 1018 is moved into the first position, the shift collar1018 is drivingly engaged with the first set of clutch gear teeth 1031of the transfer shaft 1012 and the first set of clutch gear teeth 1024of the first end portion 1023 of the input shaft 1008.

Upon having recognized one of the aforementioned conditions, theoperator of the vehicle moves or directs the vehicle to move the shiftcollar 1018 into the first position. Typically, the operator operates aswitching mechanism that causes an actuator to electronically orpneumatically move the shift fork 1066 and the associated shift collar1018 into the first position. Alternately, the operator may engage alinkage component directly coupled to the shift fork 1066 to move theshift collar 1018 into the first position. Further, the vehicle thedrive axle system 1000 is incorporated in may be configured toautomatically recognize conditions suitable for the low speed and hightorque multi-axle manner of operation and automatically move the shiftcollar 1018 into the first position using the electronic control unitwithout assistance of the operator.

Prior to engagement of the first set of clutch gear teeth 1031 of thetransfer shaft 1012 and the first set of clutch gear teeth 1024 of theinput shaft 1008 with the shift collar 1018, but after the shift collar1018 has begun to move towards the first position, the first conicalengagement surface 1045 of the first synchronizer ring 1042 contacts theengagement portion 1029 of the first end portion 1023 of the input shaft1008. Contact of the first conical engagement surface 1045 with theengagement portion 1029 causes the shift collar 1018 to accelerate toapproximately the same speed of the input shaft 1008 and the biasingmember disposed between the shift collar 1018 and the first synchronizerring 1042 to compress. Once the shift collar 1018 has been acceleratedto approximately the same speed of the input shaft 1008, movement of theshift collar 1018 into the first position is completed, and the shiftcollar 1018 is simultaneously engaged with the first set of clutch gearteeth 1031 of the transfer shaft 1012 and the first set of clutch gearteeth 1024 of the input shaft 1008.

After engagement of the first set of clutch gear teeth 1031 of thetransfer shaft 1012 and the first set of clutch gear teeth 1024 of theinput shaft 1008 with the shift collar 1018, the input shaft 1008 andthe transfer shaft 1012 rotate concurrently. Similarly, the pinioncarrier 1028 and the second end portion 1032 of the transfer shaft 1012rotate concurrently. As a result of the concurrent rotation, the set ofside gear teeth 1033 and the plurality of driving pinions 1010 arelocked with respect to one another, and the set of side gear teeth 1034of the first output gear 1016 are driven by the plurality of drivingpinions 1010 at the same speed the input shaft 1008 rotates at. Placingthe shift collar 1018 into the first position “locks out” thedifferentiating arrangement comprising the set of side gear teeth 1033,the plurality of driving pinions 1010, and the set of side gear teeth1034.

Meanwhile, the second output gear 1014 sits idle as the shift collar1018 is not engaged with the first set of clutch gear teeth 1039.Further, the axle clutch 1059 is disengaged, allowing the plurality ofdriving pinions and the pair of side gears of the second wheeldifferential 1057 to spin freely without need for the inter-axle shaft1054 to spin. In this manner, torque delivered through the input shaft1008 is transferred only to the first output axles 1052 while reducingparasitic windage losses that may be caused by needless rotation of theinter-axle shaft 1054 and the second output gear 1014.

Upon having recognized the circumstances that the low speed and hightorque multi-axle manner of operation of the drive axle system 1000 isadvantageous in, the operator of the vehicle the drive axle system 1000is incorporated in shifts the drive axle system 1000 into the secondposition. As a non-limiting example, circumstances in which the operatormay recognize as being advantageous for the low speed and high torquemulti-axle manner of operation are starting movement of the vehicle froma stopped position, operation of the vehicle along a surface having apositive gradient, and operation of the vehicle along a surface having areduced coefficient of friction. When the shift collar 1018 is movedinto the second position, the shift collar 1018 is drivingly engagedwith the first set of clutch gear teeth 1031 of the transfer shaft 1012and the first set of clutch gear teeth 1039 of the second output gear1014.

Upon having recognized one of the aforementioned conditions, theoperator of the vehicle moves or directs the vehicle to move the shiftcollar 1018 into the second position. Typically, the operator operates aswitching mechanism that causes an actuator to electronically orpneumatically move the shift fork 1066 and the associated shift collar1018 into the second position. Alternately, the operator may engage alinkage component directly coupled to the shift fork 1066 to move theshift collar 1018 into the second position. Simultaneously, the axleclutch 1059 is engaged to not allow each of the second output axles1058′ to rotate with respect to one another without rotation of theinter-axle shaft 1054. Further, the vehicle the drive axle system 1000is incorporated in may be configured to automatically recognizeconditions suitable for the low speed and high torque multi-axle mannerof operation and automatically move the shift collar 1018 into thesecond position using the electronic control unit without assistance ofthe operator.

Prior to engagement of the first set of clutch gear teeth 1031 of thetransfer shaft 1012 and the first set of clutch gear teeth 1039 of thesecond output gear 1014 with the shift collar 1018, but after the shiftcollar 1018 has begun to move towards the second position, the secondconical engagement surface 1046 of the second synchronizer ring 1043contacts the engagement portion 1038 of the second end portion 1037 ofthe second output gear 1014. Contact of the second conical engagementsurface 1046 with the engagement portion 1038 causes the shift collar1018 to accelerate to approximately the same speed of the second outputgear 1014 and the biasing member disposed between the shift collar 1018and the second synchronizer ring 1043 to compress. Once the secondoutput gear 1014 has been accelerated to approximately the same speed ofthe input shaft 1008, movement of the shift collar 1018 into the secondposition is completed, and the shift collar 1018 is simultaneouslyengaged with the first set of clutch gear teeth 1031 of the transfershaft 1012 and the first set of clutch gear teeth 1039 of the secondoutput gear 1014.

After engagement of the first set of clutch gear teeth 1031 of thetransfer shaft 1012 and the first set of clutch gear teeth 1039 of thesecond output gear 1014 with the shift collar 1018, the second outputgear 1014 and the transfer shaft 1012 rotate concurrently. Torquedelivered to the input shaft 1008 is transferred through the pluralityof driving pinions 1010 to rotate the second end portion 1032 of thetransfer shaft 1012 and the first output gear 1016. Subsequently, torqueis transferred to the inter-axle shaft 1054 through the second outputgear 1014 and the driven gear 1062 and torque is transferred to theoutput shaft 1035. Through the bevel gear pinions 1049, 1064, drivinggears 1050, 1056, and wheel differentials 1051, 1057, torque deliveredthrough the input shaft 1008 is simultaneously transferred to the firstoutput axles 1052 and the second output axles 1058.

To permit the drive axle system 1000 to operate in the low speed andhigh torque multi-axle manner of operation, gearing ratios of the drivengear 1062 with respect to the second output gear 1014 and the seconddriving gear 1056 with respect to the bevel gear pinion 1064 are higherthan a gearing ratio of the first driving gear 1050 with respect to thebevel gear pinion 1049. Resulting speed differences of the first outputaxles 1052 and the second output axles 1058 are accommodated by thedifferentiating arrangement comprising the set of side gear teeth 1033,the plurality of driving pinions 1010, and the set of side gear teeth1034, which permits operating speed differences between the first outputaxles 1052 and the second output axles 1058 to be remedied by allowingthe second end portion 1032 and the first output gear 1016 to rotatewith respect to one another through the plurality of driving pinions1010.

The drive axle system 1000 may also be used with specific shiftingprocedures for shifting the drive axle system 1000 from the firstposition into the second position.

A first specific shifting procedure may be used to accelerate theinter-axle shaft 1054 prior to completing the shift of the drive axlesystem 1000 from the first position into the second position. The firstspecific shifting procedure includes disengagement of the shift collar1065 and partial engagement of the shift collar 1018 into the secondposition. The partial engagement accelerates the inter-axle shaft 1054to an operating speed without a rotational force being applied to thesecond output axles 1058 from the inter-axle shaft 1054. Upon theinter-axle shaft 1054 being accelerated to the operating speed, theshift collar 1018 is engaged and the rotational force is applied to thesecond output axles 1058 through the inter-axle shaft 1054. Suchacceleration of the inter-axle shaft 1054 facilitates a smoothershifting of the drive axle system 1000 from the first position to thesecond position.

FIG. 11 depicts yet another embodiment of the present invention. Theembodiment shown in FIG. 11 is similar to the embodiment shown in FIG.10. Similar features of the embodiment shown in FIG. 11 are numberedsimilarly in series, with the exception of the features described below.

The first driving gear 1150 is mounted on, or connected, to an outercase portion 1170 of an axle ratio selection device 1171. The axle ratioselection device 1171 includes an inner case portion 1172, the outercase portion 1170, a plurality of case pinions 1174, and a ratioselector 1176. As is known in the art, the axle ratio selection device1171 comprises a planetary gear set; however, it is understood that theaxle ratio selection device 1171 may be any other type of multi speedselection device. The outer case portion 1170 has a toothed case end1177. The inner case portion 1172 is rotatably and concentricallymounted within the outer case portion 1170. The plurality of casepinions 1174 are rotatably mounted to an end of the inner case portion1172 and engage a case ring gear 1178 formed on an inner surface of theouter case portion 1170.

The ratio selector 1176 is a hollow member disposed about one of a pairof axle half shafts 1180. One or more bearings (not shown) and theirassociated races may be located about a portion of the ratio selector1176 to facilitate rotation of the ratio selector 1176 within the firstaxle assembly housing 1182.

The ratio selector 1176 has a first toothed end 1184 and a secondtoothed end 1186 and may be placed in a first position or a secondposition along the case pinions 1174. In the first position, the firsttoothed end 1184 of the ratio selector 1176 engages the toothed case end1177 and the case pinions 1174, “locking out” the planetary gear set ofthe axle ratio selection device 1171. When the ratio selector 1176 isplaced in the first position, the case ring gear 1178, the ratioselector 1176, and the case pinions 1174 (and thus the inner caseportion 1172), are driven at a same angular velocity.

In the second position, the first toothed end 1184 of the ratio selector1176 engages the case pinions 1174 and the second toothed end 1186 ofthe ratio selector 1176 engages a toothed portion of the first axleassembly housing 1182, fixing the first toothed end 1184 with respect tothe first axle assembly housing 1182. When the ratio selector 1176 isplaced in the second position, the case ring gear 1178 drives the casepinions 1174, and thus the inner case portion 1172, about the firsttoothed end 1184 at a reduced ratio when compared to the ratio selector1176 placed in the first position.

The ratio selector 1176 may be moved by an actuator 1188 such as apneumatic actuator, an electromechanical actuator, or a hydraulicactuator. The actuator 1188 may be connected to the anti-lock brakingsystem of the vehicle, as described below.

The first axle assembly 1104 may be utilized for the majority of thevehicle duty cycle requirements. The ratio selector 1176 of the axleratio selection device 1171 in the first position results in a gearratio of the first axle assembly 1104 selected for a high speed and lowtorque manner of operation. The gear ratio of the first axle assembly1104 having the axle ratio selection device 1171 in the first positionpreferably is employed during a single axle mode of operation, where thehigh speed and low torque manner of operation is desired. The ratioselector 1176 of the axle ratio selection device 1171 in the secondposition results in a gear ratio of the first axle assembly 1104selected for a low speed and high torque manner of operation. The gearratio of the first axle assembly 1104 having the axle ratio selectiondevice 1171 in the second position preferably corresponds to a gearratio of the second axle assembly 1106 and is employed during amulti-axle mode of operation, where the low speed and high torque mannerof operation is desired.

The second axle assembly 1106 may be selectively engaged when additionaltractive effort is required. By selectively disengaging and idling thesecond axle assembly 1106 using the inter-axle clutch 1118, anefficiency over a full time driven first and second axle assembly 1104,1106 is achieved by minimizing axle windage and parasitic drag losses.

The second axle assembly 1106 may be selectively and automaticallyengaged by an automated system that comprises wheel speed sensors and acontrol algorithm that eliminates the need for driver control. In such asituation, the second axle assembly 1106 can be automatically engaged atvehicle start up to proportion the drive torque between the first andsecond axle assemblies 1104, 1106. This has the effect of lowering themaximum torque on either the first and second axle assemblies 1104,1106. Further, because the shift collar 1118 may variably engage thesecond axle assembly 1106, a clutch torque capacity of the shift collar1118 can be used to limit the torque to the second axle assembly 1106,thus permitting it to be downsized compared to the first axle assembly1104.

FIG. 12 illustrates a drive axle system 1200 for a vehicle incorporatingan inter-axle differential assembly 1202. The drive axle system 1200preferably includes the inter-axle differential assembly 1202, a firstaxle assembly 1204, and a second axle assembly 1206. As shown, the driveaxle system 1200 includes the three assemblies 1202, 1204, and 1206, butit is understood the drive axle system 1200 may include fewer or moreassemblies or components.

The inter-axle differential assembly 1202 includes an input shaft 1208,a plurality of driving pinions 1210, a transfer shaft 1212, a secondoutput gear 1214, a first output gear 1216, and a shift collar 1218.Preferably, the components 1208, 1210, 1212, 1214, 1216, 1218 are formedfrom a hardened steel, however the components 1208, 1210, 1212, 1214,1216, 1218 may be formed from any other rigid material. As shown, thedrive axle system 1200 includes the six components 1208, 1210, 1212,1214, 1216, 1218 disposed in a housing 1220 but it is understood theinter-axle differential assembly 1202 may include fewer or morecomponents

The input shaft 1208 is at least partially disposed in the housing 1220.Preferably, the input shaft 1208 is an elongate cylindrical member,however the input shaft 1208 may be any other shape. Bearings 1222disposed between the input shaft 1208 and the housing 1220 and the inputshaft 1208 and the transfer shaft 1212 permit the input shaft 1208 torotate about an axis of the input shaft 1208. The input shaft 1208 has afirst end portion 1223, having a first set of clutch gear teeth 1224formed thereon, a middle portion 1225, and a second end portion 1226,having a pinion carrier 1228 disposed thereon.

The first end portion 1223 has a diameter greater than a diameter of themiddle portion 1225. The first end portion 1223 is a substantially discshaped body drivingly coupled to the input shaft 1208. Alternately, thefirst end portion 1223 may be integrally formed with the input shaft1208. The first end portion 1223 includes an engagement portion 1229formed therein adjacent an outer peripheral edge thereof. As shown, theengagement portion 1229 is a conical surface oblique to the input shaft1208, however, the engagement portion 1229 may have any other shape. Thefirst set of clutch gear teeth 1224 are formed on the first end portion1223 intermediate the input shaft 1208 and the engagement portion 1229.

The pinion carrier 1228 is a substantially disc shaped body having aplurality of pinion supports (not shown) protruding therefrom adjacent aperipheral edge of the pinion carrier 1228, however, the pinion carrier1228 may be any other rounded shape and may have a plurality of recessesor perforations formed therein. As is known in the art, the pinioncarrier 1228 is also known as a planet carrier.

The plurality of driving pinions 1210 are rotatably coupled to thepinion supports. Each of the driving pinions 1210 have gear teeth formedon an outer surface thereof. As is known in the art, each of the drivingpinions 1210 is also known as a planet gear. Preferably, bearings aredisposed between each of the driving pinions 1210 and the pinionsupports, however, the driving pinions 1210 may be directly mounted onthe pinion supports.

The transfer shaft 1212 is a hollow shaft concentrically disposed aboutthe input shaft 1208. Preferably, the transfer shaft 1212 is a hollowelongate cylindrical member, however the transfer shaft 1212 may be anyother shape. Bearings 1222 disposed between the transfer shaft 1212 andthe housing 1220 and the input shaft 1208 and the transfer shaft 1212permit the transfer shaft 1212 to rotate about an axis of the transfershaft 1212. The axis of the transfer shaft 1212 is concurrent with theaxis of the input shaft 1208. The transfer shaft 1212 has a first endportion 1230, having a first set of clutch gear teeth 1231 formed on anouter surface thereof, and a second end portion 1232, having a secondset of gear teeth 1233 formed on an outer surface thereof.

The first end portion 1230 and the second end portion 1232 aresubstantially disc shaped bodies having an outer diameter greater than adiameter of the transfer shaft 1212. The first end portion 1230 and thesecond end portion 1232 are drivingly coupled to the transfer shaft1212. Alternately, the first end portion 1230 and the second end portion1232 may be integrally formed with the transfer shaft 1212 and may havea diameter substantially equal to the transfer shaft 1212. Similarly,the first set of clutch gear teeth 1231 and the second set of gear teeth1233 may be formed directly in the transfer shaft 1212. As is known inthe art, the second end portion 1232 having the gear teeth 1233 is knownas a sun gear. The second set of gear teeth 1233 are engaged with theplurality of driving pinions 1210 and the first set of clutch gear teeth1231 are disposed adjacent the first set of clutch gear teeth 1231 ofthe input shaft 1208.

The second output gear 1214 is a gear concentrically disposed about theinput shaft 1208 and the transfer shaft 1212. The second output gear1214 has a central perforation having a diameter greater than a diameterof the transfer shaft 1212. The second output gear 1214 is asubstantially disc shaped body having a first end portion 1234, a secondend portion 1235 defining an outer diameter of the second output gear1214, and an engagement portion 1236. Bearings (not shown) disposedbetween the transfer shaft 1212 and the second output gear 1214 permitthe second output gear 1214 to rotate about an axis of the second outputgear 1214. The axis of the second output gear 1214 is concurrent withthe axis of the input shaft 1208. A first set of clutch gear teeth 1237are formed on the first end portion 1234 adjacent the first set ofclutch gear teeth 1231 of the transfer shaft 1212. A second set of gearteeth 1238 are formed on the second end portion 1235.

The engagement portion 1236 is formed in the second output gear 1214intermediate the first end portion 1234 and the second end portion 1235.As shown, the engagement portion 1236 is a conical surface oblique tothe input shaft 1208; however, the engagement portion 1236 may have anyother shape.

The shift collar 1218 is concentrically disposed about the input shaft1208 and the transfer shaft 1212. The shift collar 1218 includes a setof inner clutch collar teeth 1239 formed on an inner surface thereof, afirst synchronizer ring 1240, and a second synchronizer ring 1241. Theset of inner clutch collar teeth 1239 are engaged with the first set ofclutch gear teeth 1231 of the transfer shaft 1212. The shift collar 1218can be slidably moved along the axis of the input shaft 1208 as directedmanually by an operator of the vehicle or automatically by an electroniccontrol unit (not shown) while maintaining engagement of the innerclutch collar teeth 1239 and the first set of clutch gear teeth 1231. Ashift fork 1242 disposed in an annular recess formed in the shift collar1218 moves the shift collar 1218 along the axis of the input shaft 1208into a first position, a second position, or a neutral position. A shiftmechanism (not shown), which is drivingly engaged with the shift fork1242, is actuated to position the shift fork 1242 as directed manuallyby an operator of the vehicle or automatically by the electronic controlunit. Consequently, the shift fork 1242 positions the shift collar 1218into the first position, the second position, or the neutral position.In the first position, the shift collar 1218 is drivingly engaged withthe first set of clutch gear teeth 1231 of the transfer shaft 1212 andthe first set of clutch gear teeth 1224 of the input shaft 1208. In thesecond position, the shift collar 1218 is drivingly engaged with thefirst set of clutch gear teeth 1231 of the transfer shaft 1212 and thefirst set of clutch gear teeth 1237 of the second output gear 1214. Inthe neutral position, the inner clutch collar teeth 1239 of the shiftcollar 1218 are only drivingly engaged with the first set of clutch gearteeth 1231 of the transfer shaft 1212. It is understood the shift collar1218, the clutch gear teeth 1224, 1231, 1237, 1239, the synchronizerrings 1240, 1241, and the engagement portions 1229, 1236 may besubstituted with any clutching device that permits selective engagementof a driving and a driven part.

The first synchronizer ring 1240 is an annular body coupled to the shiftcollar 1218 adjacent the first end portion 1223 of the input shaft 1208.The first synchronizer ring 1240 has a first conical engagement surface1243. Alternately, the first synchronizer ring 1240 may have anengagement surface having any other shape. A biasing member (not shown)is disposed between the shift collar 1218 and the first synchronizerring 1240 to urge the first synchronizer ring 1240 away from the shiftcollar 1218. When the shift collar 1218 is moved from the secondposition into the first position, the first conical engagement surface1243 contacts the engagement portion 1229 of the first end portion 1223of the input shaft 1208. As the shift collar 1218 moves towards thefirst set of clutch gear teeth 1224 of the input shaft 1208, the biasingmember is compressed while the shift collar 1218 engages the first setof clutch gear teeth 1231 of the transfer shaft 1212 and before theshift collar 1218 engages the first set of clutch gear teeth 1224 of theinput shaft 1208.

The second synchronizer ring 1241 is an annular body coupled to theshift collar 1218 adjacent the first end portion 1234 of the secondoutput gear 1214. The second synchronizer ring 1241 has a second conicalengagement surface 1244. Alternately, the second synchronizer ring 1241may have an engagement surface having any other shape. A biasing member(not shown) is disposed between the shift collar 1218 and the secondsynchronizer ring 1241 to urge the second synchronizer ring 1241 awayfrom the shift collar 1218. When the shift collar 1218 is moved from thefirst position into the second position, the second conical engagementsurface 1244 contacts the engagement portion 1236 of the first endportion 1234 of the second output gear 1214. As the shift collar 1218moves towards the first set of clutch gear teeth 1237 of the secondoutput gear 1214, the biasing member is compressed while the shiftcollar 1218 engages the first set of clutch gear teeth 1231 of thetransfer shaft 1212 and before the shift collar 1218 engages the firstset of clutch gear teeth 1237 of the second output gear 1214.

The first output gear 1216 is a gear concentrically disposed about theinput shaft 1208 and the pinion carrier 1228. The first output gear 1216has a central recess having a diameter greater than an outer diameter ofthe pinion carrier 1228. The first output gear 1216 is a substantiallycup shaped body having an inner surface having gear teeth 1245 formedon. As is known in the art, the first output gear 1216 is known as aring gear. The gear teeth 1245 are engaged with the gear teeth formed onthe outer surface of each of the driving pinions 1210.

The first output gear 1216 includes an output shaft 1246 drivinglycoupled thereto. Alternately, the first output gear 1216 may beintegrally formed with the output shaft 1246. The output shaft 1246 iscollinear with the input shaft 1208. Bearings 1222 disposed between theoutput shaft 1246 and the housing 1220 support the first output gear1216 and permit the output shaft 1246 to rotate about an axis of theoutput shaft 1246.

A bevel gear pinion 1247 is drivingly coupled to the output shaft 1246opposite the first output gear 1216. Alternately, the bevel gear pinion1247 may be integrally formed with the output shaft 1246. As is known inthe art, the bevel gear pinion 1247 has gear teeth formed on an outersurface thereof. The bevel gear pinion 1247 may be one of a hypoid gear,a spiral bevel gear, a straight bevel gear, or any other gear known tothose skilled in the art.

The first axle assembly 1204 includes the bevel gear pinion 1247, afirst driving gear 1248, a first wheel differential 1249, and a firstpair of output axles 1250. Preferably, the components 1247, 1248, 1249,1250 are formed from a hardened steel, however the components 1247,1248, 1249, 1250 may be formed from any other rigid material. As shown,the first axle assembly 1204 includes the four components 1247, 1248,1249, 1250 disposed in a first axle housing 1251 but it is understoodthe first axle assembly 1204 may include fewer or more components.

The first driving gear 1248 is coupled to a housing of the first wheeldifferential 1249 by a plurality of fasteners or a weld and is rotatableabout an axis of the first pair of output axles 1250 within the firstaxle housing 1251. Alternately, the first driving gear 1248 may beintegrally formed with the first wheel differential 1249. As is known inthe art, the first driving gear 1248 has gear teeth formed on an outersurface thereof. The first driving gear 1248 may be one of a hypoidgear, a spiral bevel gear, a straight bevel gear, or any other gearknown to those skilled in the art. The first driving gear 1248 isdrivingly engaged with the bevel gear pinion 1247 and has a first gearratio. As a non-limiting example, the first gear ratio may be a 2.42:1ratio, but it is understood that other ratios may be used. The outputshaft 1246 is drivingly engaged with the first driving gear 1248 of thefirst axle assembly 1204 through a single gear mesh.

The first wheel differential 1249 is a bevel gear style differential asis known in the art having a plurality of driving pinions and a pair ofside gears drivingly engaged with the first pair of output axles 1250.The first wheel differential 1249 is rotatably disposed within the firstaxle housing 1251 about the axis of the first pair of output axles 1250.Alternately, other styles of differentials may be used in place of thefirst wheel differential 1249.

The first pair of output axles 1250 are elongate cylindrical membershaving a common axis rotatably mounted within the first axle housing1251. Bearings 1222 disposed between the first pair of output axles 1250and the first axle housing 1251 permit the first pair of output axles1250 to rotate therein. The side gears of the first wheel differential1249 are disposed on first ends of each of the first output axles 1250and wheels (not shown) are disposed on second ends of each of the firstoutput axles 1250.

The second axle assembly 1206 includes an inter-axle shaft 1252, asecond driving gear 1253, a second wheel differential 1254, a pair ofsecond output axles 1256, and an axle clutch 1257. Preferably, thecomponents 1252, 1253, 1254, 1256, 1257 are formed from a hardenedsteel, however the components 1252, 1253, 1254, 1256, 1257 may be formedfrom any other rigid material. As shown, the second axle assembly 1206includes the five components 1252, 1253, 1254, 1256, 1257 disposed in asecond axle housing 1258 but it is understood the second axle assembly1206 may include fewer or more components.

The inter-axle shaft 1252 comprises at least one elongate cylindricalmember drivingly engaged with the second output gear 1214 through adriven gear 1259 coupled to the inter-axle shaft 1252. As illustrated,the inter-axle shaft 1252 comprises a plurality of elongate cylindricalmembers connected by joints. Bearings 1222 disposed between theinter-axle shaft 1252 and the housing 1220 permit the inter-axle shaft1252 to rotate therein.

A bevel gear pinion 1260 is drivingly coupled to the inter-axle shaft1252 opposite the driven gear 1259. As is known in the art, the bevelgear pinion 1259 has gear teeth formed on an outer surface thereof. Thebevel gear pinion 1260 may be one of a hypoid gear, a spiral bevel gear,a straight bevel gear, or any other gear known to those skilled in theart.

The second driving gear 1253 is a ring style bevel gear as is known inthe art having a set of gear teeth engaged with the gear teeth formed onthe bevel gear pinion 1260. The second driving gear 1253 is coupled to ahousing of the second wheel differential 1254 by a plurality offasteners or a weld and is rotatable about an axis of the pair of secondoutput axles 1256 within the second axle housing 1258. Alternately, thesecond driving gear 1253 may be integrally formed with the second wheeldifferential 1254. The second driving gear 1253 is drivingly engagedwith the bevel gear pinion 1260 and has a second gear ratio. As anon-limiting example, the second gear ratio may be a 3.55:1 ratio, butit is understood that other ratios may be used. The second gear ratio isa lower gear ratio than the first gear ratio.

The second wheel differential 1254 is a bevel gear style differential asis known in the art having a plurality of driving pinions and a pair ofside gears drivingly engaged with the pair of second output axles 1256.The second wheel differential 1254 is rotatably disposed within thesecond axle housing 1258 about the axis of the pair of second outputaxles 1256. Alternately, other styles of differentials may be used inplace of the second wheel differential 1254.

The pair of second output axles 1256 are elongate cylindrical membershaving a common axis rotatably mounted within the second axle housing1258. Bearings 1222 disposed between the pair of second output axles1256 and the second axle housing 1258 permit the first pair of secondoutput axles 1256 to rotate therein. The side gears of the second wheeldifferential 1254 are disposed on first ends of each of the secondoutput axles 1256 and wheels (not shown) are disposed on second ends ofeach of the second output axles 1256.

The axle clutch 1257 is a dog style clutch that divides one of thesecond output axles 1256 into first and second portions. Alternately,the axle clutch 1257 may be a component of the second wheel differential1254 which engages a side gear of the second wheel differential 1254 andone of the second output axles 1256. The axle clutch 1257 may also be aplate style clutch or any other style clutch. A shift collar 1262slidingly disposed on a first component of the axle clutch 1257selectively engages a plurality of teeth formed thereon withcorresponding teeth formed on a first component and a second componentof the axle clutch 1257. The shift collar 1262 is urged into an engagedposition or a disengaged position by a shift fork 1264. When the axleclutch 1257 is in the engaged position, the first portion of one of thesecond output axles 1256 is drivingly engaged with the second portion ofone of the second output axles 1256.

In use, the drive axle system 1200 facilitates a low speed and hightorque multi-axle manner of operation and a high speed and low torquesingle axle manner of operation. The manner of operation of the driveaxle system 1200 is determined by a position of the shift collar 1218.The drive axle system 1200 balances a rotational difference between thefirst output gear 1216 and the second output gear 1214 caused by adifference between the first gear ratio and the second gear ratio withthe inter-axle differential assembly 1202, wherein the balancing of therotational difference between the first output gear 1216 and the secondoutput gear 1214 provides a cumulative gear ratio for the first axleassembly 1204 and the second axle assembly 1206. The cumulative gearratio is intermediate the first gear ratio and the second gear ratio.

Upon having recognized the circumstances that the high speed and lowtorque single axle manner of operation of the drive axle system 1200 isadvantageous in, the operator of the vehicle the drive axle system 1200is incorporated in shifts the drive axle system 1200 into the firstposition. As a non-limiting example, circumstances in which the operatormay recognize as being advantageous for the high speed and low torquesingle axle manner of operation are operation of the vehicle notburdened by a load and operation of the vehicle at highway speeds. Whenthe shift collar 1218 is moved into the first position, the shift collar1218 is drivingly engaged with the first set of clutch gear teeth 1231of the transfer shaft 1212 and the first set of clutch gear teeth 1224of the first end portion 1223 of the input shaft 1208.

Upon having recognized one of the aforementioned conditions, theoperator of the vehicle moves or directs the vehicle to move the shiftcollar 1218 into the first position. Typically, the operator operates aswitching mechanism that causes an actuator to electronically orpneumatically move the shift fork 1242 and the associated shift collar1218 into the first position. Alternately, the operator may engage alinkage component directly coupled to the shift fork 1242 to move theshift collar 1218 into the first position. Further, the vehicle thedrive axle system 1200 is incorporated in may be configured toautomatically recognize conditions suitable for the low speed and hightorque multi-axle manner of operation and automatically move the shiftcollar 1218 into the first position using the electronic control unitwithout assistance of the operator.

Prior to engagement of the first set of clutch gear teeth 1231 of thetransfer shaft 1212 and the first set of clutch gear teeth 1224 of theinput shaft 1208 with the shift collar 1218, but after the shift collar1218 has begun to move towards the first position, the first conicalengagement surface 1243 of the first synchronizer ring 1240 contacts theengagement portion 1229 of the first end portion 1223 of the input shaft1208. Contact of the first conical engagement surface 1243 with theengagement portion 1229 causes the shift collar 1218 to accelerate toapproximately the same speed of the input shaft 1208 and the biasingmember disposed between the shift collar 1218 and the first synchronizerring 1240 to compress. Once the shift collar 1218 has been acceleratedto approximately the same speed of the input shaft 1208, movement of theshift collar 1218 into the first position is completed, and the shiftcollar 1218 is simultaneously engaged with the first set of clutch gearteeth 1231 of the transfer shaft 1212 and the first set of clutch gearteeth 1224 of the input shaft 1208.

After engagement of the first set of clutch gear teeth 1231 of thetransfer shaft 1212 and the first set of clutch gear teeth 1224 of theinput shaft 1208 with the shift collar 1218, the input shaft 1208 andthe transfer shaft 1212 rotate concurrently. Similarly, the pinioncarrier 1228 and the second end portion 1232 of the transfer shaft 1212rotate concurrently. As a result of the concurrent rotation, the gearteeth 1233 and the driving pinions 1210 are locked with respect to oneanother, and the first output gear 1216 is driven by the driving pinions1210 at the same speed the input shaft 1208 rotates at. Placing theshift collar 1218 into the first position “locks out” the planetaryarrangement comprising the gear teeth 1233, the driving pinions 1210,and the first output gear 1216.

Meanwhile, the second output gear 1214 sits idle as the shift collar1218 is not engaged with the first set of clutch gear teeth 1237.Further, the axle clutch 1257 is disengaged, allowing the plurality ofdriving pinions and the pair of side gears of the second wheeldifferential 1254 to spin freely without need for the inter-axle shaft1252 to spin. In this manner, torque delivered through the input shaft1208 is transferred only to the first output axles 1250 while reducingparasitic windage losses that may be caused by needless rotation of theinter-axle shaft 1252 and the second output gear 1214.

Upon having recognized the circumstances that the low speed and hightorque multi-axle manner of operation of the drive axle system 1200 isadvantageous in, the operator of the vehicle the drive axle system 1200is incorporated in shifts the drive axle system 1200 into the secondposition. As a non-limiting example, circumstances in which the operatormay recognize as being advantageous for the low speed and high torquemulti-axle manner of operation are starting movement of the vehicle froma stopped position, operation of the vehicle along a surface having apositive gradient, and operation of the vehicle along a surface having areduced coefficient of friction. When the shift collar 1218 is movedinto the second position, the shift collar 1218 is drivingly engagedwith the first set of clutch gear teeth 1231 of the transfer shaft 1212and the first set of clutch gear teeth 1237 of the second output gear1214.

Upon having recognized one of the aforementioned conditions, theoperator of the vehicle moves or directs the vehicle to move the shiftcollar 1218 into the second position. Typically, the operator operates aswitching mechanism that causes an actuator to electronically orpneumatically move the shift fork 1242 and the associated shift collar1218 into the second position. Alternately, the operator may engage alinkage component directly coupled to the shift fork 1242 to move theshift collar 1218 into the second position. Simultaneously, the axleclutch 1257 is engaged to not allow each of the second output axles 1256to rotate with respect to one another without rotation of the inter-axleshaft 1252. Further, the vehicle the drive axle system 1200 isincorporated in may be configured to automatically recognize conditionssuitable for the low speed and high torque multi-axle manner ofoperation and automatically move the shift collar 1218 into the secondposition using the electronic control unit without assistance of theoperator.

Prior to engagement of the first set of clutch gear teeth 1231 of thetransfer shaft 1212 and the first set of clutch gear teeth 1237 of thesecond output gear 1214 with the shift collar 1218, but after the shiftcollar 1218 has begun to move towards the second position, the secondconical engagement surface 1244 of the second synchronizer ring 1241contacts the engagement portion 1236 of the second end portion 1235 ofthe second output gear 1214. Contact of the second conical engagementsurface 1244 with the engagement portion 1244 causes the shift collar1218 to accelerate to approximately the same speed of the second outputgear 1214 and the biasing member disposed between the shift collar 1218and the second synchronizer ring 1241 to compress. Once the secondoutput gear 1214 has been accelerated to approximately the same speed ofthe input shaft 1208, movement of the shift collar 1218 into the secondposition is completed, and the shift collar 1218 is simultaneouslyengaged with the first set of clutch gear teeth 1231 of the transfershaft 1212 and the first set of clutch gear teeth 1237 of the secondoutput gear 1214.

After engagement of the first set of clutch gear teeth 1231 of thetransfer shaft 1212 and the first set of clutch gear teeth 1237 of thesecond output gear 1214 with the shift collar 1218, the second outputgear 1214 and the transfer shaft 1212 rotate concurrently. Torquedelivered to the input shaft 1208 is transferred through the pluralityof driving pinions 1210 to rotate the second end portion 1232 of thetransfer shaft 1212 and the first output gear 1216. Subsequently, torqueis transferred to the inter-axle shaft 1252 through the second outputgear 1214 and the driven gear 1259 and torque is transferred to theoutput shaft 1246. Through the bevel gear pinions 1247, 1260, drivinggears 1248, 1259, and wheel differentials 1249, 1254, torque deliveredthrough the input shaft 1208 is simultaneously transferred to the firstoutput axles 1250 and the second output axles 1256.

The planetary arrangement comprising the gear teeth 1233, the drivingpinions 1210, and the first output gear 1216 results in an unequaldistribution of torque between the first output axles 1250 and thesecond output axles 1256. As a non-limiting example, the planetaryarrangement may result in about 70% of the torque exerted on the inputshaft 1208 being transferred to the first output axles 1250 and about30% of the torque exerted on the input shaft 1208 being transferred tothe second output axles 1256. To remedy the unequal distribution oftorque, gearing ratios of the driven gear 1259 with respect to thesecond output gear 1214 and the second driving gear 1253 with respect tothe bevel gear pinion 1260 are configured to compensate for the unequaldistribution of torque between the first output axles 1250 and thesecond output axles 1256. Resulting speed differences of the firstoutput axles 1250 and the second output axles 1256 are accommodated bythe planetary arrangement, which permits operating speed differencesbetween the first output axles 1250 and the second output axles 1256 tobe remedied by allowing the second end portion 1232 and the first outputgear 1216 to rotate with respect to one another through the plurality ofdriving pinions 1210. The gearing ratios of the driven gear 1259 withrespect to the second output gear 1214 may be of an equal ratio, anoverdrive ratio, or an underdrive ratio. As a non-limiting example, aratio of the second output gear 1214 to the driven gear 1259 may be1.6:1, but it is understood that other ratios may be used.

The drive axle system 1200 may also be used with specific shiftingprocedures for shifting the drive axle system 1200 from the firstposition into the second position.

A first specific shifting procedure may be used to accelerate theinter-axle shaft 1252 prior to completing the shift of the drive axlesystem 1200 from the first position into the second position. The firstspecific shifting procedure includes disengagement of the shift collar1262 and partial engagement of the shift collar 1218 into the secondposition. The partial engagement accelerates the inter-axle shaft 1252to an operating speed without a rotational force being applied to thesecond output axles 1256 from the inter-axle shaft 1252. Upon theinter-axle shaft 1252 being accelerated to the operating speed, theshift collar 1262 is engaged and the rotational force is applied to thesecond output axles 1256 through the inter-axle shaft 1252. Suchacceleration of the inter-axle shaft 1252 facilitates a smoothershifting of the drive axle system 1200 from the first position to thesecond position.

FIG. 13 depicts yet another embodiment of the present invention. Theembodiment shown in FIG. 13 is similar to the embodiment shown in FIG.12. Similar features of the embodiment shown in FIG. 12 are numberedsimilarly in series, with the exception of the features described below.

FIG. 13 illustrates a drive axle system 1300 for a vehicle incorporatingan inter-axle differential assembly 1202. The drive axle system 1300preferably includes the inter-axle differential assembly 1302, a firstaxle assembly 1304, and a second axle assembly 1306. As shown, the driveaxle system 1300 includes the three assemblies 1302, 1304, and 1306, butit is understood the drive axle system 1300 may include fewer or moreassemblies or components.

The inter-axle differential assembly 1302 includes an input shaft 1308,a plurality of driving pinions 1310, a transfer shaft 1312, a secondoutput gear 1314, a first output gear 1316, and a shift collar 1318.Preferably, the components 1308, 1310, 1312, 1314, 1316, 1318 are formedfrom a hardened steel, however the components 1308, 1310, 1312, 1314,1316, 1318 may be formed from any other rigid material. As shown, thedrive axle system 1300 includes the six components 1308, 1310, 1312,1314, 1316, 1318 disposed in a housing 1320 but it is understood theinter-axle differential assembly 1302 may include fewer or morecomponents

The input shaft 1308 is at least partially disposed in the housing 1320.Preferably, the input shaft 1308 is an elongate member, however theinput shaft 1308 may be any other shape. Bearings 1322 disposed betweenthe input shaft 1308 and the housing 1320 permit the input shaft 1308 torotate about an axis of the input shaft 1308. The input shaft 1308 has afirst end portion 1323, a middle portion 1324, and a second end portion1325, having a pinion carrier 1326, a first set of clutch gear teeth1327, and an engagement portion 1328 formed thereon.

The second end portion 1325 is a substantially hollow body having adiameter greater than a diameter of the first end portion 1323 and themiddle portion 1324. The second end portion 1325 is drivingly coupled tothe input shaft 1308. Alternately, the second end portion 1325 may beintegrally formed with the input shaft 1308.

The pinion carrier 1326 is a substantially disc shaped body drivinglycoupled to the second end portion 1325 of the input shaft 1308. Thepinion carrier 1326 includes a plurality of pinion supports 1329protruding from a first side of the pinion carrier 1326 into the secondend portion 1325 of the input shaft 1308. The engagement portion 1328 isformed on a second side of the pinion carrier 1326. As is known in theart, the pinion carrier 1226 is also known as a planet carrier.

The engagement portion 1328 is a conical surface oblique to the inputshaft 1308, however, the engagement portion 1328 may have any othershape. The first set of clutch gear teeth 1227 are formed on the pinioncarrier 1326 radially inward from the engagement portion 1328.

The plurality of driving pinions 1310 are rotatably coupled to thepinion supports 1330. Each of the driving pinions 1310 have gear teethformed on an outer surface thereof. As is known in the art, each of thedriving pinions 1310 is also known as a planet gear. Preferably,bearings are disposed between each of the driving pinions 1310 and thepinion supports 1329, however, the driving pinions 1310 may be directlymounted on the pinion supports.

The transfer shaft 1312 is a hollow shaft rotatably disposed in thehousing 1320 and having an axis of rotation concurrent with the axis ofrotation of the input shaft 1308. Preferably, the transfer shaft 1312 isa hollow elongate cylindrical member, however the transfer shaft 1312may be any other shape. Bearings (not shown) disposed between thetransfer shaft 1312 and pinion carrier 1326 permit the transfer shaft1312 to rotate about an axis of the transfer shaft 1312. The transfershaft 1312 has a first end portion 1330, having a first set of clutchgear teeth 1331 formed on an outer surface thereof, and a second endportion 1332, having a second set of gear teeth 1333 formed on an outersurface thereof.

The first end portion 1330 and the second end portion 1332 aresubstantially disc shaped bodies having an outer diameter greater than adiameter of the transfer shaft 1312. The first end portion 1330 and thesecond end portion 1332 are drivingly coupled to the transfer shaft1312. Alternately, the first end portion 1330 and the second end portion1332 may be integrally formed with the transfer shaft 1312 and may havea diameter substantially equal to the transfer shaft 1312. Similarly,the first set of clutch gear teeth 1331 and the second set of gear teeth1333 may be formed directly in the transfer shaft 1312. As is known inthe art, the second end portion 1332 having the gear teeth 1333 is knownas a sun gear. The second set of gear teeth 1333 are engaged with theplurality of driving pinions 1310 and the first set of clutch gear teeth1331 are disposed adjacent the first set of clutch gear teeth 1327 ofthe pinion carrier 1326.

The second output gear 1314 is a gear concentrically disposed about aportion of the transfer shaft 1312. The second output gear 1314 has acentral perforation having a diameter greater than a diameter of thetransfer shaft 1312. The second output gear 1314 is a substantially discshaped body having a first end portion 1334, a second end portion 1335defining an outer diameter of the second output gear 1314, and anengagement portion 1336. Bearings 1322 disposed between the secondoutput gear 1314 and the housing 1320 permit the second output gear 1314to rotate about an axis of the second output gear 1314. The axis of thesecond output gear 1314 is concurrent with the axis of the input shaft1308. A first set of clutch gear teeth 1337 are formed on the first endportion 1334 adjacent the first set of clutch gear teeth 1331 of thetransfer shaft 1312. A second set of gear teeth 1338 are formed on thesecond end portion 1335.

The engagement portion 1336 is formed in the second output gear 1314intermediate the first end portion 1334 and the second end portion 1335.As shown, the engagement portion 1336 is a conical surface oblique tothe input shaft 1308; however, the engagement portion 1336 may have anyother shape.

The shift collar 1318 is concentrically disposed about the transfershaft 1312. The shift collar 1318 includes a set of inner clutch collarteeth 1339 formed on an inner surface thereof, a first synchronizer ring1340, and a second synchronizer ring 1341. The set of inner clutchcollar teeth 1339 are engaged with the first set of clutch gear teeth1331 of the transfer shaft 1312. The shift collar 1318 can be slidablymoved along the axis of the input shaft 1308 as directed manually by anoperator of the vehicle or automatically by an electronic control unit(not shown) while maintaining engagement of the inner clutch collarteeth 1339 and the first set of clutch gear teeth 1331. A shift fork1342 disposed in an annular recess formed in the shift collar 1318 movesthe shift collar 1318 along the axis of the input shaft 1308 into afirst position, a second position, or a neutral position. A shiftmechanism (not shown), which is drivingly engaged with the shift fork1342, is actuated to position the shift fork 1342 as directed manuallyby an operator of the vehicle or automatically by the electronic controlunit. Consequently, the shift fork 1342 positions the shift collar 1318into the first position, the second position, or the neutral position.In the first position, the shift collar 1318 is drivingly engaged withthe first set of clutch gear teeth 1331 of the transfer shaft 1312 andthe first set of clutch gear teeth 1327 of the pinion carrier 1326. Inthe second position, the shift collar 1318 is drivingly engaged with thefirst set of clutch gear teeth 1331 of the transfer shaft 1312 and thefirst set of clutch gear teeth 1337 of the second output gear 1314. Inthe neutral position, the inner clutch collar teeth 1339 of the shiftcollar 1318 are only drivingly engaged with the first set of clutch gearteeth 1331 of the transfer shaft 1312. It is understood the shift collar1318, the clutch gear teeth 1327, 1331, 1337, 1339, the synchronizerrings 1340, 1341, and the engagement portions 1328, 1336 may besubstituted with any clutching device that permits selective engagementof a driving and a driven part.

The first synchronizer ring 1340 is an annular body coupled to the shiftcollar 1318 adjacent the engagement portion 1328 of the pinion carrier1326. The first synchronizer ring 1340 has a first conical engagementsurface 1343. Alternately, the first synchronizer ring 1340 may have anengagement surface having any other shape. A biasing member (not shown)is disposed between the shift collar 1318 and the first synchronizerring 1340 to urge the first synchronizer ring 1340 away from the shiftcollar 1318. When the shift collar 1318 is moved from the secondposition into the first position, the first conical engagement surface1343 contacts the engagement portion 1328 of the pinion carrier 1326. Asthe shift collar 1318 moves towards the first set of clutch gear teeth1327 of the input shaft 1308, the biasing member is compressed while theshift collar 1318 engages the first set of clutch gear teeth 1331 of thetransfer shaft 1312 and before the shift collar 1318 engages the firstset of clutch gear teeth 1327 of the pinion carrier 1326.

The second synchronizer ring 1341 is an annular body coupled to theshift collar 1318 adjacent the first end portion 1334 of the secondoutput gear 1314. The second synchronizer ring 1341 has a second conicalengagement surface 1344. Alternately, the second synchronizer ring 1341may have an engagement surface having any other shape. A biasing member(not shown) is disposed between the shift collar 1318 and the secondsynchronizer ring 1341 to urge the second synchronizer ring 1341 awayfrom the shift collar 1318. When the shift collar 1318 is moved from thefirst position into the second position, the second conical engagementsurface 1344 contacts the engagement portion 1336 of the second outputgear 1314. As the shift collar 1318 moves towards the first set ofclutch gear teeth 1337 of the second output gear 1314, the biasingmember is compressed while the shift collar 1318 engages the first setof clutch gear teeth 1331 of the transfer shaft 1312 and before theshift collar 1318 engages the first set of clutch gear teeth 1337 of thesecond output gear 1314.

The first output gear 1316 is a gear concentrically disposed within thesecond end portion 1325 of the input shaft 1308. The first output gear1316 is a substantially cup shaped body having an inner surface havinggear teeth 1345 formed on. As is known in the art, the first output gear1316 is known as a ring gear. The gear teeth 1345 are engaged with thegear teeth formed on the outer surface of each of the driving pinions1310.

The first output gear 1316 includes an output shaft 1346 drivinglycoupled thereto. Alternately, the first output gear 1316 may beintegrally formed with the output shaft 1346. The output shaft 1346 iscollinear with the input shaft 1308. Bearings 1322 disposed between theoutput shaft 1346 and the housing 1320 support the output shaft 1346 andpermit the output shaft 1346 to rotate about an axis of the output shaft1346.

In use, the drive axle system 1300 facilitates a low speed and hightorque multi-axle manner of operation and a high speed and low torquesingle axle manner of operation. The manner of operation of the driveaxle system 1300 is determined by a position of the shift collar 1318.The drive axle system 1300 balances a rotational difference between thefirst output gear 1316 and the second output gear 1314 caused by adifference between the first gear ratio and the second gear ratio withthe inter-axle differential assembly 1302, wherein the balancing of therotational difference between the first output gear 1316 and the secondoutput gear 1314 provides a cumulative gear ratio for the first axleassembly 1304 and the second axle assembly 1306. The cumulative gearratio is intermediate the first gear ratio and the second gear ratio.

Upon having recognized the circumstances that the high speed and lowtorque single axle manner of operation of the drive axle system 1300 isadvantageous in, the operator of the vehicle the drive axle system 1300is incorporated in shifts the drive axle system 1300 into the firstposition. As a non-limiting example, circumstances in which the operatormay recognize as being advantageous for the high speed and low torquesingle axle manner of operation are operation of the vehicle notburdened by a load and operation of the vehicle at highway speeds. Whenthe shift collar 1318 is moved into the first position, the shift collar1318 is drivingly engaged with the first set of clutch gear teeth 1331of the transfer shaft 1312 and the first set of clutch gear teeth 1327of the pinion carrier 1326.

Upon having recognized one of the aforementioned conditions, theoperator of the vehicle moves or directs the vehicle to move the shiftcollar 1318 into the first position. Typically, the operator operates aswitching mechanism that causes an actuator to electronically orpneumatically move the shift fork 1342 and the associated shift collar1318 into the first position. Alternately, the operator may engage alinkage component directly coupled to the shift fork 1342 to move theshift collar 1318 into the first position. Further, the vehicle thedrive axle system 1300 is incorporated in may be configured toautomatically recognize conditions suitable for the low speed and hightorque multi-axle manner of operation and automatically move the shiftcollar 1318 into the first position using the electronic control unitwithout assistance of the operator.

Prior to engagement of the first set of clutch gear teeth 1331 of thetransfer shaft 1312 and the first set of clutch gear teeth 1327 of theinput shaft 1308 with the shift collar 1318, but after the shift collar1318 has begun to move towards the first position, the first conicalengagement surface 1343 of the first synchronizer ring 1340 contacts theengagement portion 1328 of the pinion carrier 1326. Contact of the firstconical engagement surface 1343 with the engagement portion 1328 causesthe shift collar 1318 to accelerate to approximately the same speed ofthe input shaft 1308 and the biasing member disposed between the shiftcollar 1318 and the first synchronizer ring 1340 to compress. Once theshift collar 1318 has been accelerated to approximately the same speedof the input shaft 1308, movement of the shift collar 1318 into thefirst position is completed, and the shift collar 1318 is simultaneouslyengaged with the first set of clutch gear teeth 1331 of the transfershaft 1312 and the first set of clutch gear teeth 1327 of the pinioncarrier 1326.

After engagement of the first set of clutch gear teeth 1331 of thetransfer shaft 1312 and the first set of clutch gear teeth 1327 of thepinion carrier 1326 with the shift collar 1318, the input shaft 1308 andthe transfer shaft 1312 rotate concurrently. Similarly, the pinioncarrier 1326 and the second end portion 1332 of the transfer shaft 1312rotate concurrently. As a result of the concurrent rotation, the gearteeth 1333 and the driving pinions 1310 are locked with respect to oneanother, and the first output gear 1316 is driven by the driving pinions1310 at the same speed the input shaft 1308 rotates at. Placing theshift collar 1318 into the first position “locks out” the planetaryarrangement comprising the gear teeth 1333, the driving pinions 1310,and the first output gear 1316.

Meanwhile, the second output gear 1314 sits idle as the shift collar1318 is not engaged with the first set of clutch gear teeth 1337.Further, the axle clutch 1357 is disengaged, allowing the plurality ofdriving pinions and the pair of side gears of the second wheeldifferential 1354 to spin freely without need for the inter-axle shaft1352 to spin. In this manner, torque delivered through the input shaft1308 is transferred only to the first output axles 1350 while reducingparasitic windage losses that may be caused by needless rotation of theinter-axle shaft 1352 and the second output gear 1314.

Upon having recognized the circumstances that the low speed and hightorque multi-axle manner of operation of the drive axle system 1300 isadvantageous in, the operator of the vehicle the drive axle system 1300is incorporated in shifts the drive axle system 1300 into the secondposition. As a non-limiting example, circumstances in which the operatormay recognize as being advantageous for the low speed and high torquemulti-axle manner of operation are starting movement of the vehicle froma stopped position, operation of the vehicle along a surface having apositive gradient, and operation of the vehicle along a surface having areduced coefficient of friction. When the shift collar 1318 is movedinto the second position, the shift collar 1318 is drivingly engagedwith the first set of clutch gear teeth 1331 of the transfer shaft 1312and the first set of clutch gear teeth 1337 of the second output gear1314.

Upon having recognized one of the aforementioned conditions, theoperator of the vehicle moves or directs the vehicle to move the shiftcollar 1318 into the second position. Typically, the operator operates aswitching mechanism that causes an actuator to electronically orpneumatically move the shift fork 1342 and the associated shift collar1318 into the second position. Alternately, the operator may engage alinkage component directly coupled to the shift fork 1342 to move theshift collar 1318 into the second position. Simultaneously, the axleclutch 1357 is engaged to not allow each of the second output axles 1356to rotate with respect to one another without rotation of the inter-axleshaft 1352. Further, the vehicle the drive axle system 1300 isincorporated in may be configured to automatically recognize conditionssuitable for the low speed and high torque multi-axle manner ofoperation and automatically move the shift collar 1318 into the secondposition using the electronic control unit without assistance of theoperator.

Prior to engagement of the first set of clutch gear teeth 1331 of thetransfer shaft 1312 and the first set of clutch gear teeth 1337 of thesecond output gear 1314 with the shift collar 1318, but after the shiftcollar 1318 has begun to move towards the second position, the secondconical engagement surface 1344 of the second synchronizer ring 1341contacts the engagement portion 1336 of the second end portion 1335 ofthe second output gear 1314. Contact of the second conical engagementsurface 1344 with the engagement portion 1344 causes the shift collar1318 to accelerate to approximately the same speed of the second outputgear 1314 and the biasing member disposed between the shift collar 1318and the second synchronizer ring 1341 to compress. Once the secondoutput gear 1314 has been accelerated to approximately the same speed ofthe input shaft 1308, movement of the shift collar 1318 into the secondposition is completed, and the shift collar 1318 is simultaneouslyengaged with the first set of clutch gear teeth 1331 of the transfershaft 1312 and the first set of clutch gear teeth 1337 of the secondoutput gear 1314.

After engagement of the first set of clutch gear teeth 1331 of thetransfer shaft 1312 and the first set of clutch gear teeth 1337 of thesecond output gear 1314 with the shift collar 1318, the second outputgear 1314 and the transfer shaft 1312 rotate concurrently. Torquedelivered to the input shaft 1308 is transferred through the pluralityof driving pinions 1310 to rotate the second end portion 1332 of thetransfer shaft 1312 and the first output gear 1316. Subsequently, torqueis transferred to the inter-axle shaft 1352 through the second outputgear 1314 and the driven gear 1359 and torque is transferred to theoutput shaft 1346. Through the bevel gear pinions 1347, 1360, drivinggears 1348, 1359, and wheel differentials 1349, 1354, torque deliveredthrough the input shaft 1308 is simultaneously transferred to the firstoutput axles 1350 and the second output axles 1356.

The planetary arrangement comprising the gear teeth 1333, the drivingpinions 1310, and the first output gear 1316 results in an unequaldistribution of torque between the first output axles 1350 and thesecond output axles 1356. As a non-limiting example, the planetaryarrangement may result in about 70% of the torque exerted on the inputshaft 1308 being transferred to the first output axles 1350 and about30% of the torque exerted on the input shaft 1308 being transferred tothe second output axles 1356. To remedy the unequal distribution oftorque, gearing ratios of the driven gear 1359 with respect to thesecond output gear 1314 and the second driving gear 1353 with respect tothe bevel gear pinion 1360 are configured to compensate for the unequaldistribution of torque between the first output axles 1350 and thesecond output axles 1356. Resulting speed differences of the firstoutput axles 1350 and the second output axles 1356 are accommodated bythe planetary arrangement, which permits operating speed differencesbetween the first output axles 1350 and the second output axles 1356 tobe remedied by allowing the second end portion 1332 and the first outputgear 1316 to rotate with respect to one another through the plurality ofdriving pinions 1310. The gearing ratios of the driven gear 1359 withrespect to the second output gear 1314 may be of an equal ratio, anoverdrive ratio, or an underdrive ratio. As a non-limiting example, aratio of the second output gear 1314 to the driven gear 1359 may be1.6:1, but it is understood that other ratios may be used.

As is known in the art and as used herein with respect to each of theembodiments disclosed, the first pinion shaft 106, the first axle inputshaft 206, 406, 506, 606, 706, 806, 906, the first axle shaft 306, andthe input shaft 1008, 1108, 1208, 1308 may comprise a plurality of shaftsections. Further, it is understood that the first pinion shaft 106, thefirst axle input shaft 206, 406, 506, 606, 706, 806, 906, the first axleshaft 306, and the input shaft 1008, 1108, 1208, 1308 may include aplurality of joints disposed thereon. As a first non-limiting example,it is understood that the plurality of shaft sections of the firstpinion shaft 106, the first axle input shaft 206, 406, 506, 606, 706,806, 906, the first axle shaft 306, and the input shaft 1008, 1108,1208, 1308 may be joined by a clutching device such as a plate clutch, ashift collar, or any other clutching device. As further non-limitingexamples, it is understood the plurality of shaft sections of the firstpinion shaft 106, the first axle input shaft 206, 406, 506, 606, 706,806, 906, the first axle shaft 306, and the input shaft 1008, 1108,1208, 1308 may be joined through a locked differential, may pass througha differential, and may enclose a differential.

In accordance with the provisions of the patent statutes, the presentinvention has been described in what is considered to represent itspreferred embodiments. However, it should be noted that the inventioncan be practiced otherwise than as specifically illustrated anddescribed without departing from its spirit or scope.

What is claimed is:
 1. A drive axle system, comprising: a first shaftcomprising at least one shaft section; a bevel gear inter-axledifferential comprising a first side gear, a driving spider, and asecond side gear, the driving spider drivingly engaged with the firstshaft; a first axle assembly comprising a first wheel differential, afirst driving gear coupled to the first wheel differential and drivinglyengaged with the second side gear of the bevel gear inter-axledifferential, and a first pair of output axles drivingly engaged withthe first wheel differential; a second axle assembly comprising a secondwheel differential, a second driving gear coupled to the second wheeldifferential, a second pair of output axles drivingly engaged with thesecond wheel differential, and a first clutching device disposed on anddividing one of the second pair of output axles into first and secondportions; and a second clutching device having at least a first positionand a second position, wherein the second clutching device in the firstposition drivingly engages the second driving gear with the first sidegear of the bevel gear inter-axle differential and the second clutchingdevice in the second position drivingly engages the first side gear ofthe bevel gear inter-axle differential with the driving spider of thebevel gear inter-axle differential.
 2. The drive axle system accordingto claim 1, wherein the first shaft is drivingly engaged with the firstdriving gear of the first axle assembly through a single gear mesh. 3.The drive axle system according to claim 1, wherein the first clutchingdevice comprises a second shift collar concentrically disposed about oneof the second pair of output axles, the first clutching device having afirst position and a second position, the first clutching device in thefirst position drivingly engaging the first portion with the secondportion of one of the second pair of output axles and the firstclutching device in the second position disengaging the first portionfrom the second portion of one of the second pair of output axles. 4.The drive axle system according to claim 1, wherein the second clutchingdevice comprises a shift collar concentrically disposed about the firstshaft, a first synchronizer, and a second synchronizer, the firstsynchronizer engaging an output gear and an inter-axle shaft with thesecond driving gear of the second axle assembly when the shift collar isin the first position and the second synchronizer engaging the firstshaft when the shift collar is in the second position.
 5. The drive axlesystem according to claim 4, wherein first shaft includes a firstengagement portion for engaging with the second synchronizer and theoutput gear includes a second engagement portion for engaging with thefirst synchronizer.
 6. The drive axle system according to claim 1,wherein the first axle assembly further comprises an axle ratioselection device, the axle ratio selection device having at least twofirst axle ratios and the second axle assembly has a second axle ratio,one of the at least two first axle ratios different from the second axleratio.
 7. The drive axle system according to claim 6, wherein the axleratio selection device comprises a planetary gear set.
 8. The drive axlesystem according to claim 7, wherein the axle ratio selection device hasa first position and a second position, the axle ratio selection devicein the first position having a sun gear in a non-rotatable position andthe axle ratio selection device in the second position having theplanetary gear set in a locked up position.
 9. The drive axle systemaccording to claim 1, wherein the first axle assembly has a first axleratio and the second axle assembly has a second axle ratio, the firstaxle ratio different from the second axle ratio.
 10. A drive axlesystem, comprising: a first shaft comprising at least one shaft section;a bevel gear inter-axle differential comprising a first side gear, adriving spider, and a second side gear, the driving spider drivinglyengaged with the first shaft; a first axle assembly comprising a firstwheel differential, a first driving gear coupled to the first wheeldifferential and drivingly engaged with the second side gear of thebevel gear inter-axle differential, and a first pair of output axlesdrivingly engaged with the first wheel differential; a second axleassembly comprising a second wheel differential, a second driving gearcoupled to the second wheel differential, a second pair of output axlesdrivingly engaged with the second wheel differential, and a firstclutching device disposed on and dividing one of the second pair ofoutput axles into first and second portions; and a second clutchingdevice having at least a first position and a second position, thesecond clutching device comprising a shift collar concentricallydisposed about the first shalt, a first synchronizer, and a secondsynchronizer, wherein the first synchronizer engages an output gear andan inter-axle shaft with the second driving gear of the second axleassembly to drivingly engage the second driving gear with the first sidegear of the bevel gear inter-axle differential when the shift collar isin the first position and the second synchronizer engages the firstshaft to drivingly engage the first side gear of the bevel gearinter-axle differential with the driving spider of the bevel gearinter-axle differential when the shift collar is in the second position.11. The drive axle system according to claim 10, wherein the first shaftis drivingly engaged with the first driving gear of the first axleassembly through a single gear mesh.
 12. The drive axle system accordingto claim 10, wherein the first clutching device comprises a second shiftcollar concentrically disposed about one of the second pair of outputaxles, the first clutching device having a first position and a secondposition, the first clutching device in the first position drivinglyengaging the first portion with the second portion of one of the secondpair of output axles and the first clutching device in the secondposition disengaging the first portion from the second portion of one ofthe second pair of output axles.
 13. The drive axle system according toclaim 10, wherein the first shaft includes a first engagement portionfor engaging with the second synchronizer and the output gear includes asecond engagement portion for engaging with the first synchronizer. 14.The drive axle system according to claim 10, wherein the first axleassembly further comprises an axle ratio selection device, the axleratio selection device having at least two first axle ratios and thesecond axle assembly has a second axle ratio, one of the at least twofirst axle ratios different from the second axle ratio.
 15. A drive axlesystem, comprising: a first shaft comprising an engagement portion andan end portion; a bevel gear inter-axle differential comprising a firstside gear, a driving spider, and a second side gear, the driving spiderdrivingly engaged with the first shaft; a first clutching deviceconcentric with the first shaft, the first clutching device selectivelyengaging the driving spider of the bevel gear inter-axle differentialwith the engagement portion of the first shaft; an output shaftcomprising a first end portion and a second end portion; a first axleassembly comprising a first wheel differential, a first driving gearcoupled to the first wheel differential and drivingly engaged with thesecond end portion of the output shaft, and a first pair of output axlesdrivingly engaged with the first wheel differential; a second axleassembly comprising a second wheel differential, a second driving gearcoupled to the second wheel differential and drivingly engaged with thefirst side gear of the bevel gear inter-axle differential, a second pairof output axles drivingly engaged with the second wheel differential,and an axle clutching device disposed on and dividing one of the secondpair of output axles into first and second portions; and a secondclutching device concentric with the first shaft, the second clutchingdevice having at least a first position and a second position, whereinthe second clutching device in the first position selectively engagesthe second side gear with the first end portion of the output shaft andthe second clutching device in the second position selectively engagesthe first end portion of the output shaft with the end portion of thefirst shaft.
 16. The drive axle system according to claim 15, whereinthe first shaft is drivingly engaged with the first driving gear of thefirst axle assembly through a single gear mesh.
 17. The drive axlesystem according to claim 15, wherein the first axle assembly has afirst axle ratio and the second axle assembly has a second axle ratio,the first axle ratio different from the second axle ratio.
 18. The driveaxle system according to claim 15, wherein the second clutching deviceincludes a synchronizer for facilitating variable engagement between thesecond side gear and the first end portion of the output shaft.
 19. Thedrive axle system according to claim 18, wherein the first clutchingdevice includes a synchronizer for facilitating variable engagementbetween the driving spider of the bevel gear inter-axle differential andthe engagement portion of the first shaft.